Recombinase Polymerase Amplification

ABSTRACT

The present invention features novel, diverse, hybrid and engineered recombinase enzymes, and the utility of such proteins with associated recombination factors for carrying out DNA amplification assays. The present invention also features different recombinase ‘systems’ having distinct biochemical activities in DNA amplification assays, and differing requirements for loading factors, single-stranded DNA binding proteins (SSBs), and the quantity of crowding agent employed.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 11/800,318 filed, May 4, 2007, which claims the benefit of U.S. Provisional Application No. 60/798,060, filed May 4, 2006. The contents of the foregoing applications are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to novel hybrid and engineered recombinase enzymes, and the use of such enzymes for the amplification of nucleic acids. More specifically, the present invention relates to the use of T6, Rb69, Aeh1, and KVP40 hybrid and engineered proteins, and the use of such proteins in recombinase polymerase amplification assays.

BACKGROUND

Recombinase Polymerase Amplification (RPA) is a process in which recombinase-mediated targeting of oligonucleotides to DNA targets is coupled to DNA synthesis by a polymerase (Armes and Stemple, U.S. application Ser. No. 10/371,641). RPA depends upon components of the cellular DNA replication and repair machinery. The notion of employing some of this machinery for in vitro DNA amplification has existed for some time (Zarling et al. U.S. Pat. No. 5,223,414), however the concept has not transformed to a working technology until recently as, despite a long history of research in the area of recombinase function involving principally the E. coli RecA protein, in vitro conditions permitting sensitive amplification of DNA have only recently been determined (Piepenburg et al. U.S. patent application Ser. No. 10/931,916, also Piepenburg et al., PlosBiology 2006). Development of a ‘dynamic’ recombination environment having adequate rates of both recombinase loading and unloading that maintains high levels of recombination activity for over an hour in the presence of polymerase activity proved technically challenging and needed specific crowding agents, notably PEG molecules of high molecular weight (Carbowax 20M molecular weight 15-20,000, and others described herein, particularly PEG molecular weight 35,000), in combination with the use of recombinase-loading factors, specific strand-displacing polymerases and a robust energy regeneration system.

The RPA technology depended critically on the empirical finding that high molecular weight polyethylene glycol species (particularly >10,000 Daltons or more) very profoundly influenced the reaction behaviour. It has previously been discovered that polyethylene glycol species ranging in size from at least molecular weight 12,000 to 100,000 stimulate RPA reactions strongly. While it is unclear how crowding agents influence processes within an amplification reaction, a large variety of biochemical consequences are attributed to crowding agents and are probably key to their influence on RPA reactions.

Crowding agents have been reported to enhance the interaction of polymerase enzymes with DNA (Zimmerman and Harrison, 1987), to improve the activity of polymerases (Chan E. W. et al., 1980), to influence the kinetics of RecA binding to DNA in the presence of SSB (Layery and Kowalczykowski, 1992). Crowding agents are reported to have marked influence on systems in which co-operative binding of monomers is known to occur such as during rod and filament formation (Rivas et al., 2003) by increasing association constants by potentially several orders of magnitude (see Minton, 2001). In the RPA system multiple components rely on co-operative binding to nucleic acids, including the formation of SSB filaments, recombinase filaments, and possibly the condensation of loading agents such as UvsY. Crowding agents are also well known to enhance the hybridization of nucleic acids (Amasino, 1986), and this is a process that is also necessary within RPA reactions. Finally, and not least, PEG is known to drive the condensation of DNA molecules in which they change from elongated structures to compact globular or toroidal forms, thus mimicking structures more common in many in vivo contexts (see Lerman, 1971; also see Vasilevskaya. et. al., 1995; also see Zinchenko and Anatoly, 2005) and also to affect the supercoiling free energy of DNA (Naimushin et al., 2001).

Without intending to be bound by theory, it is likely that crowding agents influence the kinetics of multiple protein-protein, protein-nucleic acid, and nucleic acid-nucleic acid interactions within the reaction. The dependence on large molecular weight crowding agents for the most substantial reaction improvement (probably greater than about 10,000 Daltons in size) may reflect a need to restrict the crowding effect to reaction components over a certain size (for example oligonucleotides, oligonucleotide:protein filaments, duplex products, protein components) while permitting efficient diffusion of others (say nucleotides, smaller peptides such as UvsY). Further, it may also be that the high molecular weight preference might reflect findings elsewhere that as PEG molecular weight increases the concentration of metal ions required to promote DNA condensation decreases. In any case it is an empirical finding that RPA is made effective by the use of high molecular weight polyethylene glycols.

In addition to a need for specific type of ‘crowded’ reaction conditions as described above (reaction in the presence of crowding agents), effective RPA reaction kinetics depend on a high degree of ‘dynamic’ activity within the reaction with respect to recombinase-DNA interactions. In other words, the available data which includes (i) reaction inhibition by ATP-γ-S, or removal of the acidic C terminus of RecA or UvsX, and (ii) inhibition by excessive ATP (Piepenburg et al., 2006) suggest that not only is it important that recombinase filaments can be formed rapidly, but also important that they can disassemble quickly. This data is consistent with predictions made in earlier U.S. patent application Ser. No. 10/371,641. Rapid filament formation ensures that at any given moment there will be a high steady state level of functional recombinase-DNA filaments, while rapid disassembly ensures that completed strand exchange complexes can be accessed by polymerases.

Other processes must be adequately supported in the reaction environment in addition to highly dynamic recombinase loading/unloading. For the benefit of later discussions there now follows a more complete list of factors to note when considering how RPA reaction may be affected by changes in activity/properties of the components:

1. As stated above there must be a high overall level of active, correctly loaded, recombinase-DNA filaments at any given moment to ensure rapid kinetics of invasion and strand exchange. This is required to drive rapid reaction kinetics at low target numbers early in the reaction, as predicted by standard bi-molecular reaction kinetics, as well as to ensure non-limiting quantities of active filaments late in the reaction when targets become highly abundant and could easily out-titrate the loaded filaments.

2. Filaments must be dynamic, capable of rapid disassembly as well as assembly, to ensure that strand exchange processes work rapidly, and to avoid filament ‘lock-up’ in unproductive protein-DNA conformations (should they arise).

3. Recombinases should have a strong preference for single-stranded DNA, and a relatively weaker preference for double-stranded DNA. This ensures the correct partitioning of recombinase onto the oligonucleotides, and is very important in the late phase of the reaction when significant quantities of duplex DNA accumulate. This duplex DNA may otherwise compete too effectively for recombinase and slow the reaction too rapidly. A difference in disassembly rates on duplex DNA would also enhance factor (ii) insofar as accelerating disassembly of productive exchange complexes. Observations consistent with ‘out-titration’ activity of excess duplex DNA, such as decreases in reaction rate late in the reaction, or if excess DNA is present early in the reaction, have been made.

4. Hybridization of single-stranded DNA's to one another must be supported under any given reaction condition. RPA has the potential to generate single-stranded DNA products which may only be converted to new duplex targets following hybridization of the complementary priming oligonucleotide to initiate DNA synthesis. As saturating quantities of single-stranded DNA binding proteins (i.e. loading proteins, single-stranded DNA binding proteins and recombinases) are present in the reaction environment, these hybridization processes must be supported/aided by these proteins. SSB's and recombinases have some melting/hybridization activities on duplex/single-stranded DNA's, and probably demonstrate differential levels of melting/hybridization activity. Thus the relative proportions of recombinase and SSB of loading may influence the rate behaviour for hybridization, and this may also depend on the species of SSB and recombinase employed. If either the SSB or recombinase does not, or only poorly, supports hybridization of single-stranded DNAs to one another, then the reaction may be compromised.

5. The temporal change in reaction composition with regard to pH, anion accumulation, generation of ADP, of AMP, pyrophosphate, and other nucleotide species may be strongly influenced by the recombinase employed. Furthermore recombinases may respond differentially to the ionic and pH environment. Rates of nucleotide hydrolysis affect the accumulation of the afore-mentioned species, and their accumulation may in turn influence the activity in the reaction of recombinases and polymerases. For example accumulation of phosphate and pyrophosphate may inhibit recombinase processes, while the accumulation of ADP (and possibly AMP) can affect DNA on-off kinetics of the recombinase. Notably bacteriophage T4 UvsX protein has been reported to hydrolyse ATP to both ADP and AMP, a property not attributed to other recombinases to date. Recombinases may also hydrolyse dATP, UTP and potentially other nucleotides. Different nucleotides may affect the DNA binding stabilities of complexes on ssDNA and dsDNA, for example dATP has been noted to increase the stability of RecA on ssDNA. Without intending to be bound by theory, the particular properties of a recombinase with respect to its DNA binding domains and nucleotide binding/catalysis domains may have significant impact on reaction rate and effectiveness in generating strong signals late in the reaction.

Previously Established RPA Conditions.

Effective RPA reactions have previously been demonstrated using both E. coli RecA (in a heterologous system with compromised gp32 protein) and with the T4 phage UvsX protein (when combined with the T4 phage UvsY protein) (Piepenburg et al., 2006). In both cases the employment of polyethylene glycol was found to be absolutely necessary for amplification to occur with any useful efficiency when templates were present at concentrations below roughly nanomolar levels (or roughly below the order of about 10¹⁰ target molecules per microliter).

Experimentation showed the importance of PEG in stimulating secondary, tertiary and yet further invasion events when using oligonucleotides directed towards the ends of linear templates, said oligonucleotide initially having a 5′ overhang relative to the initial target, but being flush to later targets due to the activity of ‘backfire’ synthesis (Piepenburg et al. U.S. Ser. No. 10/931,916). Fully embedded targets proved to be even more intractable, almost certainly due to the topological constraints associated with the recombination products caused by the outgoing strand being wound unfavourably around the newly formed duplex. Without intending to be bound by any theory, the huge increase in efficiency of initiating replication from these more unstable intermediates in the presence of PEG may depend on stability conferred by the crowding agent on the complexes, on altered DNA conformation and coiling (such as DNA condensation), on much higher association constants for the polymerase gaining access to the intermediates, and/or a very great increase in the frequency of recombination events leading to more ‘chances’ of the polymerase grabbing the intermediate and elongating.

An RPA system utilizing bacteriophage T4 UvsX, T4 UvsY, and T4gp32, a B. subtilis PolI large fragment, and PEG compound (carbowax 20M) is effective for amplifying duplex DNA sequences up to about 1 kilobase in length (Piepenburg et al., 2006). Average doubling times of as little as 40 seconds or less have been attained for fragments of roughly 300 nucleotides, and DNA accumulates to levels useful for detection by a variety of means, even when targets are initially present at levels below 10 copies. Despite this robust behaviour there exists a need for the identification of other recombinases, their associated loading components and single stranded DNA binding proteins, due to the strict necessity for very rapid kinetics and strong signals for the implementation of the RPA system in commercially useful products. The present invention meets these needs and other needs.

SUMMARY OF THE INVENTION

This disclosure provides enabling data on the use of alternative recombinase/accessory factor systems for performing RPA reactions. As evidenced herein, bacteriophage T6 UvsX, bacteriophage Rb69 UvsX, UvsY and gp32, and bacteriophage Aeh1 UvsX, UvsY, and gp32 can be employed successfully in RPA reactions. Additionally, evidence that bacteriophage KVP40 UvsX and UvsY may also be able to support RPA reactions is included, although problems were encountered in the production of KVP40 gp32 that limited this analysis. In general it was discovered that variation in the concentration of reactants must be performed to identify optimal conditions for each system, and there are observable differences in overall kinetic activity. The present invention provides evidence of limited cross-compatibility between reaction components generated from different species. In general the requirement for co-employment of UvsX and UvsY from the same or similar species was observed, while gp32 may be less stringently matched. Also provided herein are mutant and chimeric recombinase proteins, in particular the use of altered T6 and Rb69 UvsX proteins, and chimeric T4 and Rb69 UvsY proteins, and the analysis thereof. This analysis leads to identification of residues influencing the assayable behaviour of the proteins in RPA reactions. As provided herein, some, but not all, of the character of the T4 UvsX protein derives from a unique serine residue within the Walker A motif. Without intending to be bound by any theory, the resulting re-iteration of a lysine-serine dipeptide within the motif may underpin the hydrolysis of ATP to both ADP and AMP by this protein. Modification of T6 UvsX protein to contain this re-iteration results in altered (improved) RPA activity when monitored in real-time. Such modified UvsX demonstrates changed reaction kinetics when assayed by proprietary fluorescent probes, in particular exhibiting steeper fluorescent signal-generation curves during the late phase of the amplification reaction. Also provided herein is the discovery that regions of myoviridae UvsX proteins which are predicted to be equivalents to DNA binding loop 2 of E. coli are variable and impart distinctive activities UvsX hybrids used in RPA reactions. Rb69 UvsX is an unusual UvsX molecule in regard to this sequence, more closely resembling the bacterial homologs. The present invention provides a model for structure/sequence compatibility in the surface region of recombinase enzymes that binds both nucleic acids and ATP, and how this evidence may be employed to ‘tune’ and improve (alter) recombinase activity. Surprisingly it was discovered that T6 UvsX, in particular, can function moderately well with a complete absence of UvsY protein. This property may be evident for other UvsX species although less markedly. Finally the present invention provides the use of manganese ions to support RPA reactions, the use of heparin to improve signal:noise ratios, the use S. aureus Pol I as the polymerase employed in RPA reactions, and E. coli exonuclease III to process and unblock primer ends in some cases to permit elongation.

The first RPA embodiment of the invention is directed to a process (method) of recombinase polymerase amplification of a double stranded target nucleic acid molecule. In the first step of the process, a first and a second single stranded nucleic acid primer is contacted with a recombinase (e.g., UvsX), a recombinase loading agent (e.g., UvsY) and a single strand DNA binding protein (e.g., gp32) to form a first and a second nucleoprotein primer. The single stranded nucleic acid primers are specific for and are complementary to the target nucleic acid molecule. In this case each of the recombinase (e.g., UvsX), recombinase loading agent (e.g., UvsY) and single strand DNA binding protein (e.g., gp32) are derived from a myoviridae phage. Further, no more than two of the recombinase (e.g., UvsX), recombinase loading agent (e.g., UvsY) and single strand DNA binding protein (e.g., gp32) are T4 phage proteins.

In the second step, the first nucleoprotein primer is contacted to the double stranded target nucleic acid molecule to create a first D loop structure at a first portion of the double stranded target nucleic acid molecule (Step 2a). Further, the second nucleoprotein primer is contacted to the double stranded target nucleic acid molecule to create a second D loop structure at a second portion of the double stranded target nucleic acid molecule (Step 2b). The D loop structures are formed such that the 3′ ends of the first nucleic acid primer and said second nucleic acid primer are oriented toward each other on the same double stranded target nucleic acid molecule without completely denaturing the target nucleic acid molecule. It should be noted that step 2a and step 2b can be performed in any order or simultaneously.

In a D loop structure, the primer is hybridized to one strand of the double stranded target nucleic acid molecule to form a double stranded structure. The second strand of the target nucleic acid molecule is displaced by the primer. The structure resembles a capital D where the straight part of the D represents the double stranded part of the structure and the curved part of the D represents the single stranded displaced second strand of the target nucleic acid.

In the third step, the 3′ end of the first and the second nucleoprotein primer is extended with one or more polymerases capable of strand displacement synthesis and dNTPs to generate a first and second double stranded target nucleic acid molecule and a first and second displaced strand of nucleic acid. The first and second double stranded target nucleic acid molecules may serve as target nucleic acid molecules in step two during subsequent rounds of amplification.

Steps two and step 3 are repeated until a desired degree of amplification of the target nucleic acid is achieved. A desired degree of amplification may be at least 10³, 10⁴, 10⁵, 10⁶, 10⁷, 10⁸, or 10⁹ fold amplification.

During the amplification process described above, the first and second displaced strand of nucleic acid may hybridize to each other after step (c) to form a third double stranded target nucleic acid molecule.

In any of the processes of this disclosure, the recombinase (e.g., UvsX), recombinase loading agent (e.g., UvsY) and single strand DNA binding protein (e.g., gp32) may be derived from a myoviridae phage. The myoviridae phage may be, for example, T4, T2, T6, Rb69, Aeh1, KVP40, Acinetobacter phage 133, Aeromonas phage 65, cyanophage P-SSM2, cyanophage PSSM4, cyanophage S-PM2, Rb14, Rb32, Aeromonas phage 25, Vibrio phage nt-1, phi-1, Rb16, Rb43, Phage 31, phage 44RR2.8t, Rb49, phage Rb3, or phage LZ2. In a preferred embodiment, the combination of Rb69 UvsX, Rb69 UvsY and Rb69 gp32 may be used. In another preferred embodiment, the combination of Aeh1 UvsX, Aeh1 UvsY and Rb69 gp32 may be used. In another preferred embodiment, the combination of T4 UvsX, T4 UvsY and Rb69 gp32 may be used. In another preferred embodiment, the combination of T4 UvsX, Rb69 UvsY and T4 gp32 may be used.

Further, in any of the processes of this disclosure, the recombinase (e.g., UvsX), recombinase loading agent (e.g., UvsY) and single strand DNA binding protein (e.g., gp32) can each be native, hybrid or mutant proteins from the same or different myoviridae phage sources. A native protein may be a wildtype or natural variant of a protein. A mutant protein (also called a genetically engineered protein) is a native protein with natural or manmade mutations such as insertions, deletions, substitutions, or a combination thereof, that are at the N terminus, C terminus, or interior (between the N terminus and the C terminus). A hybrid protein (also called a chimeric protein) comprises sequences from at least two different organisms. For example, a hybrid UvsX protein may contain an amino acid from one species (e.g., T4) but a DNA binding loop from another species (e.g., T6). The hybrid protein may contain improved characteristics compared to a native protein. The improved characteristics may be increased or more rapid RPA amplification rate or a decreased or more controllable RPA amplification rate.

In any process of this disclosure, the recombinase (e.g., UvsX) may be a mutant UvsX. In a preferred embodiment, the mutant UvsX is an Rb69 UvsX comprising at least one mutation in the Rb69 UvsX amino acid sequence, wherein the mutation is selected from the group consisting of (a) an amino acid which is not histidine at position 64, a serine at position 64, the addition of one or more glutamic acid residues at the C-terminus, the addition of one or more aspartic acid residues at the C-terminus, and a combination thereof. In another preferred embodiment, the mutant UvsX is a T6 UvsX having at least one mutation in the T6 UvsX amino acid sequence, wherein the mutation is selected from the group consisting of (a) an amino acid which is not histidine at position 66; (b) a serine at position 66; (c) the addition of one or more glutamic acid residues at the C-terminus; (d) the addition of one or more aspartic acid residues at the C-terminus; and (e) a combination thereof.

In any process of this disclosure where a hybrid protein is used, the hybrid protein may be a UvsX protein comprising at least one region which comprises an amino acid sequence from a different UvsX species. The region may be, for example, the DNA-binding loop-2 region of UvsX.

Any of the RPA process of this disclosure may be performed in the presence of a crowding agent. The crowding agent may be selected from the group comprising polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polystyrene, Ficoll, dextran, PVP, albumin. In a preferred embodiment, the crowding agent has a molecular weight of less than 200,000 daltons. Further, the crowding agent may be present in an amount of about 0.5% to about 15% weight to volume (w/v).

Any of the RPA processes of this disclosure may be performed with a polymerase which is a large fragment polymerase. The large fragment polymerase may be selected from the group consisting of E. Coli Pol I, Bacillus subtilis Pol I, Staphylococcus aureus Pol I, and homologues thereof.

Any of the RPA processes of this disclosure may be performed in the presence of heparin. Heparin may serve as an agent to reduce the level of non-specific primer noise, and to increase the ability of E. coli exonuclease III or E. Coli exonuclease IV to rapidly polish 3′ blocking groups or terminal residues from recombination intermediates.

Further, any of the RPA processes of this disclosure may be performed with a blocked primer. A blocked primer is a primer which does not allow elongation with a polymerase. Where a blocked primer is used, an unblocking agent is also used to unblock the primer to allow elongation. The unblocking agent may be an endonuclease or exonuclease which can cleave the blocking group from the primer. Preferred unblocking agents include E. coli exonuclease III and E. coli endonuclease IV.

Any of the RPA processes of this disclosure may be performed in the presence of about 1 mM to about 3 mM divalent manganese ions. In a preferred embodiment, the manganese ions replace the magnesium ions and the reaction may be performed with or without magnesium.

Furthermore, UvsY may be optionally omitted from any of the RPA reactions of this disclosure. That is, any of the RPA reactions of this disclosure may be performed in the absence of UvsY.

The second RPA embodiment of the invention is directed to a process (method) of recombinase polymerase amplification of a double stranded target nucleic acid molecule. In the first step of the process, recombinase (e.g., UvsX), recombinase loading agent (e.g., UvsY) and single strand DNA binding protein (e.g., gp32) are contacted with a first single stranded nucleic acid primer specific for the double stranded target nucleic acid molecule to form a population of first nucleoprotein primer, wherein the recombinase (e.g., UvsX), recombinase loading agent (e.g., UvsY) and single strand DNA binding protein (e.g., gp32) are each derived from a myoviridae phage, and wherein no more than two of the recombinase (e.g., UvsX), recombinase loading agent (e.g., UvsY) and single strand DNA binding protein (e.g., gp32) are T4 phage proteins.

In the second step, the first nucleoprotein primer is contacted with the double stranded target nucleic acid molecule to form a first D loop structure at a first portion of said double stranded target nucleic acid molecule without completely denaturing the target nucleic acid molecule;

In the third step, the 3′ end of the first nucleoprotein primer is extended with one or more polymerases capable of strand displacement synthesis and dNTPs to generate a double stranded target nucleic acid molecule and a displaced strand of nucleic acid molecule;

In the fourth step, a second single stranded nucleic acid primer is hybridized to the displaced strand of nucleic acid molecule to form a hybridized second single stranded nucleic acid primer;

In the fifth step, the hybridized second single stranded nucleic acid primer is elongated to generate a double stranded target nucleic acid molecule;

The second through fifth steps of the reaction is continued until a desired degree of amplification is reached.

All other aspects of this second RPA embodiment is similar to that of the first RPA embodiment including the desired degree of amplification and the choice of proteins (recombinase, loading agent, single stranded DNA binding protein) etc. These parameters are described above for the first RPA embodiment. We have found, surprisingly, that RPA would function even if only one of the nucleic acid primers was coated with recombinase/recombinase loading agent/single stranded DNA binding protein. That is, an RPA may be performed with one primer which is uncoated and one primer which is coated with any one or a combination of recombinase, recombinase loading agent, and single stranded DNA binding protein.

The production of a coated primer and an uncoated primer may be made in a number of methods. In one method, only one primer is contacted to any one or a combination of recombinase, recombinase loading agent, and single stranded DNA binding protein before commencement of RPA. In another method, both primers are contacted to any one or a combination of recombinase, recombinase loading agent, and single stranded DNA binding protein. However, one primer is incapable of attaching sufficient protein to be able to generate a D loop on a target double stranded nucleic acid. This may be because the primer is too short or contain unusual nucleic acids such that it cannot bind sufficient protein for recombination. Nevertheless, to our surprise, RPA is possible even if only one primer is capable of forming D loops. RPA is possible in this circumstance because the primer which cannot form a D loop can hybridize to any displaced strand generated from the D loop capable primer (the recombinase coated primer) to initiate DNA synthesis.

Another embodiment of the invention is directed to a mutant or hybrid Rb69 UvsX protein with an amino acid sequence selected from the group consisting of (a) an amino acid which is not histidine at position 64; (b) a serine at position 64; (c) the addition of one or more glutamic acid residues at the C-terminus; (d) the addition of one or more aspartic acid residues at the C-terminus; (e) the replacement of DNA-binding loop-2 region with a DNA-binding loop-2 region from a UvsX protein which is not Rb69 UvsX; and (f) a combination thereof. An example of such mutants or hybrids may be found, for example, in SEQ ID NO:114, SEQ ID NO:115, SEQ ID NO:116, SEQ ID NO:117, SEQ ID NO:118, SEQ ID NO:119, SEQ ID NO:120, or SEQ ID NO:121.

Another embodiment of the invention is directed to a mutant or hybrid T6 UvsX protein having at least one mutation in the amino acid sequence, wherein the mutation is selected from the group consisting of (a) an amino acid which is not histidine at position 66; (b) a serine at position 66; (c) the addition of one or more glutamic acid residues at the C-terminus; (d) the addition of one or more aspartic acid residues at the C-terminus; (e) the replacement of DNA-binding loop-2 region with a DNA-binding loop-2 region from a UvsX protein which is not T6 UvsX; (f) a valine at position 164, (g) a serine at position 166, and (h) a combination thereof. See, for example, SEQ ID NO:105 and SEQ ID NO:106.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic representation of clones used to generate variant UvsX, UvsY and gp32 proteins.

FIG. 2 shows a primary sequence alignment of bacteriophage T4 UvsX with E. coli recA. T4 UvsX sequence is: MSDLKSRLIK ASTSKLTAEL TASKFFNEKD VVRTKIPMMN IALSGEITGG MQSGLLILAG PSKSFKSNFG LTMVSSYMRQ YPDAVCLFYD SEFGITPAYL RSMGVDPERV IHTPVQSLEQ LRIDMVNQLD AIERGEKVVV FIDSLGNLAS KKETEDALNE KVVSDMTRAK TMKSLFRIVT PYFSTKNIPC IAINHTYETQ EMFSKTVMGG GTGPMYSADT VFIIGKRQIK DGSDLQGYQF VLNVEKSRTV KEKSKFFIDV KFDGGIDPYS GLLDMALELG FVVKPKNGWY AREFLDEETG EMIREEKSWR AKDTNCTTFW GPLFKHQPFR DAIKRAYQLG AIDSNEIVEA EVDELINSKV EKFKSPESKS KSAADLETDL EQLSDMEEFN E (SEQ ID NO:1). The E. Coli RecA sequence is as follows: MAIDENKQKA LAAALGQIEK QFGKGSIMRL GEDRSMDVET ISTGSLSLDI ALGAGGLPMG RIVEIYGPES SGKTTLTLQV IAAAQREGKT CAFIDAEHAL DPIYARKLGV DIDNLLCSQP DTGEQALEIC DALARSGAVD VIVVDSVAAL TPKAEIEGEI GDSHMGLAAR MMSQAMRKLA GNLKQSNTLL IFINQIRMKI GVMFGNPETT TGGNALKFYA SVRLDIRRIG AVKEGENVVG SETRVKVVKN KIAAPFKQAE FQILYGEGIN FYGELVDLGV KEKLIEKAGA WYSYKGEKIG QGKANATAWL KDNPETAKEI EKKVRELLLS NPNSTPDFSV DDSEGVAETN EDF (SEQ ID NO:2).

FIG. 3 shows a representative 3-D structure of a model of an active E. coli recA filament with superimposition and labelling of equivalent T4 UvsX residues based on primary sequence alignment. FIG. 3A is a screenshot looking down the axis of the model RecA filament with the central hole being the approximate location of bound DNA. The approximate location of the Walker A motif and mobile DNA binding loops is indicated for a single subunit and is on the surface facing the nucleic acid. FIGS. 3B and 3C are two zoomed shots taken of the region to which ATP is bound on the surface indicated in 3A.

FIG. 4 shows the primary sequence alignment of T4 and T6 g32 and UvsY proteins. The T6 gp32 sequence is as follows: MFKRKSTAEL AAQMAKLAGN KGGFSSEDKG EWKLKLDNAG NGQAVIRFLP SKNDEQAPFA ILVNHGFKKN GKWYIETCSS THGDYDSCPV CQYISKNDLY NTDNKEYSLV KRKTSYWANI LVVKDPAAPE NEGKVFKYRF GKKIWDKINA MIAVDVEMGE TPVDVTCPWE GANFVLKVKQ VSGFSNYDES KFLNQSAIPN IDDESFQKEL FEQMVDLSEM TSKDKFKSFE ELSTKFSQVM GTAAMGGAAA TAAKKADKVA DDLDAFNVDD FNTKTEDDFM SSSSGSSSSA DDTDLDDLLN DL (SEQ ID NO:3). The T4 gp32 sequence is as follows: MFKRKSTAEL AAQMAKLNGN KGFSSEDKGE WKLKLDNAGN GQAVIRFLPS KNDEQAPFAI LVNHGFKKNG KWYIETCSST HGDYDSCPVC QYISKNDLYN TDNKEYSLVK RKTSYWANIL VVKDPAAPEN EGKVFKYRFG KKIWDKINAM IAVDVEMGET PVDVTCPWEG ANFVLKVKQV SGFSNYDESK FLNQSAIPNI DDESFQKELF EQMVDLSEMT SKDKFKSFEE LNTKFGQVMG TAVMGGAAAT AAKKADKVAD DLDAFNVDDF NTKTEDDFMS SSSGSSSSAD DTDLDDLLND L (SEQ ID NO:4). The T4 UvsY sequence is as follows: MRLEDLQEEL KKDVFIDSTK LQYEAANNVM LYSKWLNKHS SIKKEMLRIE AQKKVALKAR LDYYSGRGDG DEFSMDRYEK SEMKTVLSAD KDVLKVDTSL QYWGILLDFC SGALDAIKSR GFAIKHIQDM RAFEAGK (SEQ ID NO:5). The T6 UvsY sequence is as follows: MRLEDLQEEL KKDVFIDSTK LQYEAANNVM LYSKWLNKHS SIKKEMLRID AQKKVALKAK LDYYSGRGDG DEFSMDRYEK SEMKTVLSAD KDVLKVDTSL QYWGILLDFC SGALDAIKSR GFAIKHIQDM RAFEAGK (SEQ ID NO:6).

FIG. 5 shows the primary sequence alignment of diverse UvsX proteins. The T4UvsX sequence is as follows: MSDLKSRLIK ASTSKLTAEL TASKFFNEKD VVRTKIPMMN IALSGEITGG MQSGLLILAG PSKSFKSNFG LTMVSSYMRQ YPDAVCLFYD SEFGITPAYL RSMGVDPERV IHTPVQSLEQ LRIDMVNQLD AIERGEKVVV FIDSLGNLAS KKETEDALNE KVVSDMTRAK TMKSLFRIVT PYFSTKNIPC IAINHTYETQ EMFSKTVMGG GTGPMYSADT VFIIGKRQIK DGSDLQGYQF VLNVEKSRTV KEKSKFFIDV KFDGGIDPYS GLLDMALELG FVVKPKNGWY AREFLDEETG EMIREEKSWR AKDTNCTTFW GPLFKHQPFR DAIKRAYQLG AIDSNEIVEA EVDELINSKV EKFKSPESKS KSAADLETDL EQLSDMEEFN E (SEQ ID NO:7). The t6UvsX sequence is as follows: MSIADLKSRL IKASTSKMTA ELTTSKFFNE KDVIRTKIPM LNIAISGAID GGMQSGLTIF AGPSKHFKSN MSLTMVAAYL NKYPDAVCLF YDSEFGITPA YLRSMGVDPE RVIHTPIQSV EQLKIDMVNQ LEAIERGEKV IVFIDSIGNM ASKKETEDAL NEKSVADMTR AKSLKSLFRI VTPYFSIKNI PCVAVNHTIE TIEMFSKTVM TGGTGVMYSA DTVFIIGKRQ IKDGSDLQGY QFVLNVEKSR TVKEKSKFFI DVKFDGGIDP YSGLLDMALE LGFVVKPKNG WYAREFLDEE TGEMIREEKS WRAKDTNCTT FWGPLFKHQP FRDAIKRAYQ LGAIDSNEIV EAEVDELINS KVEKFKSPES KSKSAADLET DLEQLSDMEE FNE (SEQ ID NO:8). The Phage133UvsX sequence is as follows: MSSLKERLIK ASTSKMTAEL TKSKFFNDKT VVRTRIPMLN IAISGALNGG MQSGLTIFAG PSKHFKSNMG LTMVAAYMKA FPDAVCMFYD SEFGITPAYL KAMGVDPDRV IHTPVQSVEQ LKIDMTNQLE EVKRGEKVIV FIDSIGNLAS KKETEDALNE KTTADMTRAK ALKSLFRIVT PYFSIKDIPC VAVNHTLQTL EMFSKEVMTG GTGVMYSADT VFFIGKRQVK DGTELAGYEF ILKAEKSRMV KEKSVFPITV KFDGGIDPYS GLLEMATDLG FVVKPKVGWY KRAMMVDGVM QHEEKSWRAK DTDSIDFWGP LFKHDEFRKA IETRYQLGSI ESDAEVDAEV DALIGSKTTA KISGVNFGPA ESAADKEQQL EDFVDED (SEQ ID NO:9). The Rb69 UvsX sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKHFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAINHTAMEI GGLYPKEIMG GGTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE (SEQ ID NO:10). The Aeh1UvsX sequence is as follows: MAKGIKTAKT GNLGSLMSKL AGTSSNKMSS VLADSKFFND KDCVRTRVPL LNLAMSGELD GGLTPGLTVL AGPSKHFKSN LSLVFVAAYL RKYPDAVCIF FDNEFGSTPG YFESQGVDIS RVIHCPFKNI EELKFDIVKK LEAIERGDRV IVFVDSIGNA ASKKEIDDAI DEKSVSDMTR AKQIKSLTRM MTPYLTVNDI PAIMVAHTYD TQEMYSKKVV SGGTGITYSS DTVIIIGRQQ EKDGKELLGY NFVLNMEKSR FVKEQSKLPL EVTFQGGINT YSGMLDIALE VGFVVKPSNG WFSRAFLDEE TGELVEEDRK WRRADTNCLE FWKPMFAHQP FKTACSDMFK LKSVAVKDEV FDEVDELFSG EAEMPVNMGR KLDTADQEEI DQLEEVDVEG SDSDELFANL D (SEQ ID NO:11). The Ae65UvsX sequence is as follows: MAKKAKVVNS GDLLERLNGT SSNKMSAMLA ESIFFNEKDT IRTRVPIINL MMSGRLDGGI TPGLTCIAGP SKHFKSNLSL VMVSAYLRKY PKAVCLFFDN EFGSTPDYFT SQGVDISRVV HCPFIDVEEL KFDIVKKLES ITRGDKVIIY IDSIGNVASK KELQDAKDEK SAQDMTRAKQ IKSLFRMVTP YLTVLDIPCI AVNHTYETQE MFSKTVMSGG TGPMYSADTV IILGKQQDKD GKELLGYNFV MNAEKSRAIK EKSKLDLMVS FEGGINTYSG LLKIAQELGF VTKPQNARYQ RNFLDLEPGE MVIPEDEKKW TEEESDSLEF WKPMFSHKPF MDAVSNAYKL KAVEVSQEVF DEVDQLFG (SEQ ID NO:12). The Kvp40UvsX sequence is as follows: MSDLMKSLKK SSTSGYAQVL SESQFMFDKD HTRTYVPAIN IAFSGEVDGG LTSGLTVLAG PSKHFKSNLG LVGVAAYLKK YPDAVCVFID TEFGITPSYL RSQGVDPDRV LHIQCESVER MKFEMANQLK DLAERKRAKK AGEEPDRVIF FIDSVGNVAS AKEIDDAQNE KSVADMSRAK QLKSLFRIIT PYFTMLDIPC IAINHTYQTQ EIYSKTVMSG GTGIMYSADT VIILGKQQEK DGKDIIGYHF IMNIEKSRFV KEKMKVPLTV TYENGIDPFS GLLDIALQTG HVVKPSNGWY QRATVDEETG EMIVEEKKYR AKETQTISFW KDIINSPTFK EGVKRIYCLG QLDESELFGE VDSLFD (SEQ ID NO:13). The Rb43UvsX sequence is as follows: MSNKALLKKL IKNSNSQSAA ILSESDVFNN ITKTRTRVPI LNLALSGAFD GGLTSGLTLF AGPSKHFKSN LGLVTVSAYL KANEDAVCLF YDSEKGVTKS YLKSMGVDPD RVVYTRITTV EQLRNDVVSQ LDALERGDKV IIFVDSVGNT ASKKELADAL SDNDKQDMTR AKALKGMFRM VTPYLADLDI PMVCICHTYD TQEMYSKKVI SGGTGLMYSA DTAIILGKQQ VKEGTEVVGY DFIMNIEKSR FVKEKSKFPL HVTYEGGISM YSGLLDLAME MNFVQTPTKG WRGRAFLNTE TGELELEEKK WRESETNSIE FWRPLFTHQP FLDAIQDKYR IPDKEITDGA ALEDLYSTDE PESNKIDLDD DIPDDIGIDQ DEEPIM (SEQ ID NO:14). The PSSM2UvsX sequence is as follows: MDFLKEIVKE IGDEYTQVAA DIQENERFID TGSYIFNGLV SGSIFGGVSS SRITAIAGES STGKTYFSLA VVKNFLDNNP DGYCLYFDTE AAVNKGLLES RGIDMNRLVV VNVVTIEEFR SKALRAVDIY LKTSEEERKP CMFVLDSLGM LSTEKEIRDA LDDKQVRDMT KSQLVKGAFR MLTLKLGQAN IPLIVTNHTY DVIGSYVPTK EMGGGSGLKY AASTIIYLSK KKEKDQKEVI GNLIKAKTHK SRLSKENKEV QIRLYYDERG LDRYYGLLEL GEIGGMWKNV AGRYEMNGKK IYAKEILKNP TEYFTDDIME QLDNIAKEHF SYGTN (SEQ ID NO:15). The PSSM4UvsX sequence is as follows: MNFLKDIAKE IGNDYASLVS EGVSAGDTAG FIDTGSYIFN ALLSGSIYGG IPNNKITAIA GETSTGKTFF CLGMVQHFLE SNPDAGVIYF ESESAISKQM IEDRGIDSNR MLLVPVTTVQ EFRLQAIKIL DKYNEQTAEE RKPLMFVLDS LGMLSTSKEV EDSEAGKETR DMTRAQVVKS IFRVLTLKLG KANVPLIVTN HTYDVVGAYI PTKEMGGGSG LKYAASTIVY LSKKKEKNGK EVVGNIIKCK TAKSRLTKEN SDVETRLYYD RGLDRYYGLL ELGEKHGVFS RKGNRVVVGD SSVYPSAILA DPDKYFTEEL MEKLDEAAAK EFRYGN (SEQ ID NO:16).

FIG. 6 shows the primary sequence alignment of diverse UvsY proteins. The T4UvsY sequence is as follows: MRLEDLQEEL KKDVFIDSTK LQYEAANNVM LYSKWLNKHS SIKKEMLRIE AQKKVALKAR LDYYSGRGDG DEFSMDRYEK SEMKTVLSAD KDVLKVDTSL QYWGILLDFC SGALDAIKSR GFAIKHIQDM RAFEAGK (SEQ ID NO:17). The T6UvsY sequence is as follows: MRLEDLQEEL KKDVFIDSTK LQYEAANNVM LYSKWLNKHS SIKKEMLRID AQKKVALKAK LDYYSGRGDG DEFSMDRYEK SEMKTVLSAD KDVLKVDTSL QYWGILLDFC SGALDAIKSR GFAIKHIQDM RAFEAGK (SEQ ID NO:18). The Rb69UvsY sequence is as follows: MKLEDLQEEL DADLAIDTTK LQYETANNVK LYSKWLRKHS FIRKEMLRIE TQKKTALKAR LDYYSGRGDG DEFSMDRYEK SEMKTVLAAD KDVLKIETTL QYWGILLEFC SGALDAVKSR SFALKHIQDM REFEAGQ (SEQ ID NO:19). The phage133UvsY sequence is as follows: MTLEDLQAEL KKDLVLDMTQ LQTEAAENIN LYCKWSTKYS NIRKSILSLD AQRKKHTKTK LDYYSGRGDE VSMDRYERSE MKTVLSGDAD ILTVETKIQY FTIMLEFCGN AMDAIKSRGF AIKNIIDLRQ FEAGK (SEQ ID NO:20). The Aeh1UvsY sequence is as follows: MTLDELKEEL KADLPIKLTA VQTEVAENPV LYGKWNRYLA DINREITRLD AERKKMLRDR FMFYTGRSED EVCMDVYSPT ELKTVIAGDE EVIKKNAAVE LSQAKADFCR QSMEAVRQRG FSLRAIIDCR KLEAGE (SEQ ID NO:21). The Rb43UvsY sequence is as follows: MTELKLEDLQ AELEQDMLID PLKLQSESAD IPKIWSKWLR YHSNAKKKLI QLQARKEADV KERLLYYTGR HETEMTDVIY TGSGEIKIAI NGDPKIVEVN KLIQYFELIA EFTSKALDIV KNKGYSIKNM LEIRKLESGA (SEQ ID NO:22). The Kvp40UvsY sequence is as follows: MKLQDLKAEY HEDVKIDTTA LETAAIRIPV LHAKWLAYRA DARQLLIKAE MKMEAVRKDR WLFYSGKHDD EVCDFIVEKS EMKYALAGDE ALQLAIARFQ HMKDVLSFIE EALKGISQMG FTIKHIIDNR KIESGIV (SEQ ID NO:23). The PSSM2UvsY sequence is as follows: MNLDKIQEMW ERDAVIDPDN LHDESLKIPQ LHSKYYTVYN TVTLMREKAR EQYNKTRLER HNYYTGKAPA EVYIEEPFGY KVREKDAIQR YMEADEKMSK IDLKIRYYDT TLKFLEEIIK NISNRTFQIK NAIEWNKFQA GM (SEQ ID NO:24). The PSSM4UvsY sequence is as follows: MNLEQIQEMW KKDSVIDNDL YCEESTKIPQ LHMRYMELYT TFGLMKKERE IEMKRLIREK WLYYKGKAPS SVYKELPFDL KLTTKEEVNM FIEGDDDVRK LQYKIEYVEQ CLNYLDGVLR QINNRNFQIK NAIDWTKFQN GL (SEQ ID NO:25).

FIG. 7 shows the primary sequence alignment of diverse gp32 proteins. The T4gp32 sequence is as follows: MFKRKSTAEL AAQMAKLNGN KGFSSEDKGE WKLKLDNAGN GQAVIRFLPS KNDEQAPFAI LVNHGFKKNG KWYIETCSST HGDYDSCPVC QYISKNDLYN TDNKEYSLVK RKTSYWANIL VVKDPAAPEN EGKVFKYRFG KKIWDKINAM IAVDVEMGET PVDVTCPWEG ANFVLKVKQV SGFSNYDESK FLNQSAIPNI DDESFQKELF EQMVDLSEMT SKDKFKSFEE LNTKFGQVMG TAVMGGAAAT AAKKADKVAD DLDAFNVDDF NTKTEDDFMS SSSGSSSSAD DTDLDDLLND L (SEQ ID NO:26). The T6gp32 sequence is as follows: MFKRKSTAEL AAQMAKLAGN KGGFSSEDKG EWKLKLDNAG NGQAVIRFLP SKNDEQAPFA ILVNHGFKKN GKWYIETCSS THGDYDSCPV CQYISKNDLY NTDNKEYSLV KRKTSYWANI LVVKDPAAPE NEGKVFKYRF GKKIWDKINA MIAVDVEMGE TPVDVTCPWE GANFVLKVKQ VSGFSNYDES KFLNQSAIPN IDDESFQKEL FEQMVDLSEM TSKDKFKSFE ELSTKFSQVM GTAAMGGAAA TAAKKADKVA DDLDAFNVDD FNTKTEDDFM SSSSGSSSSA DDTDLDDLLN DL (SEQ ID NO:27). The Rb69gp32 sequence is as follows: MFKRKSTADL AAQMAKLNGN KGFSSEDKGE WKLKLDASGN GQAVIRFLPA KTDDALPFAI LVNHGFKKNG KWYIETCSST HGDYDSCPVC QYISKNDLYN TNKTEYSQLK RKTSYWANIL VVKDPQAPDN EGKVFKYRFG KKIWDKINAM IAVDTEMGET PVDVTCPWEG ANFVLKVKQV SGFSNYDESK FLNQSAIPNI DDESFQKELF EQMVDLSEMT SKDKFKSFEE LNTKFNQVLG TAALGGAAAA AASVADKVAS DLDDFDKDME AFSSAKTEDD FMSSSSSDDG DLDDLLAGL (SEQ ID NO:28). The Aeh1 gp32 sequence is as follows: MSIFKRKDPS QLQQQLAAFS AKKGFESDAT EWKLTQGKDG NGAAVIRFLP AKGDNATTFV KLVNHGFQRN GKWYIENCSS THGDYDNCPA CQWIKEQNWD YNVEADKKAM YASGVTRKTA FWANILVIKD PANPDNEGKV FKFRFGKKIM DKIQAEVDVN TDLGEEPCDV TCPFEGKNFT IKIKKVGGNN NYDDSVFGKQ SQIANIEDEA YQAQLFEQMH DIMDLIAKDK FKSMEDLTTV FNRVMGAEKR SNARAADDFE KQMEQFENTP ASKPEKEDDD VPFNTGSAGT VDTDLDDLLN EI (SEQ ID NO:29). The Rb43gp32 sequence is as follows: MSFFKRQDPT KLQEQVAALK GSSGFQKDEK EWKLTLDAQK NGSAVIRFLP NRSDDELAFV RIVNHSFKKQ NQWYIENCPS THGDYDGCPV CQYITDNDLF EKAKANKGGE ADKLLGQIGR KQSFWANILV IKDPGNPENE GKVFKFRFGK KIMDKITATI AGNPDLDEPG IAVTCPFAGA NFTLKAKKVG DWPNYDDSTF GVPGPIKGID DEAVQKAIFE GMSDLRPITA PDQFKPTAEL TAKFTKVFGG GAAMGAGSSA GADLDSELNS FDADLKNFDN GNQSGSVKES GGVNQLNVGG SVPEDDTPFD LDNTSGDDDL DKLLDL (SEQ ID NO:30). The Kvp40gp32 sequence is as follows: MFKRKSPAQL QEKLEKMSSK KSFDNADEWK LTTDKLGNGS AVIRFLPAKG EDDLPFVKIF THGFKENGNW FIENCPSTID LPCPCCAANG ELWKTEIEDN QNIARKRKRT LSYWANIVVI KDDAAPENEG KVFKYRFGKK ILDKITQAAQ ADEDLGVPGM DVTCVFDGAN FSLKAKKVSG FPNYDDSKFG PSTELYGGDE AKLKEVWDAM HDLNAIIAPS AFKSEAELQK RFLQVTGAAQ PKASAAQNLE AQLNTSAPAQ ANAPKAAAKP AAASVDVDSE PVTDSVDDEL DALLADLELG DD (SEQ ID NO:31). The PSSM2gp32 sequence is as follows: MSFAKLKKQS KLGSLTQKLV KEVEKMNNTG GQGDDRLWKL EVDKGGNGYD VIRFLPAPDG EDLPFVKLYS HAFQGPGGWY IENSLTTLGQ KDPVSEFNSQ LWNNGTDAGK DTARKQKRKL TYISNIYVVK DPANPENEGK TFLYKYGKKI FDKLTAAMQP EFEDEEAIDP FDFWQGANFK LKAKNVAGYR NYDSSEFAAT SALLDDDDAM EAIWKKEYSL AELVATDQFK SYDELKTRLG YVLGNKPVRN DAETVEQEVE DVRASAPVVE TVESVSRSSA TEDEDDTLSY FAKLAES (SEQ ID NO:32). The PSSM4gp32 sequence is as follows: MSFASLKKAA SAGSTLSKLT QEIEKINQPQ QNNSADERFW KPELDKSGNG FAVIRFLPAP EGEEMPWAKV WSHAFKGPGG QWYIENSLTT IGKDDPVGEY NRELWNSGKE SDKNIARAQK RKLSYYSNIY VVSDPAHPEN EGKVFLYKYG KKIFDKLVEA MQPAFADETP LDPFNFWKGA DFKLKIRKLD GYWNYDKSEF AATSTLGGFD DSKLESIWKE GYSLTEFESA KNFKDYDALK KRLDLVLGLT IPHPTTEDES LEDLSEGKTP SSWGQEVSDF REKAVASSPV QDEEDTLSYF SRLAEED (SEQ ID NO:33).

FIG. 8 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 UvsX and T4 UvsX for amplification. Rs8179145-2 is (SEQ ID NO:34) and RS8179145-3 is (SEQ ID NO:35).

FIG. 9 is a graph showing a comparison the kinetic behaviour of T6 and T4 UvsX in an RPA reaction using SYBR green dye.

FIG. 10 is graph showing a comparison of kinetic behaviour of T6 and T4 UvsX in an RPA reaction using a fluorescent probe.

FIG. 11 is a schematic layout of novel, engineered T6 UvsX protein constructs of the present invention.

FIG. 12 a graph showing a comparison of the kinetic behaviour of T6 UvsX H66S and wild type T6 UvsX using a fluorescent probe.

FIG. 13 is a graph showing a comparison of the kinetic behaviour various T6 UvsX mutants in an RPA reaction using a fluorescent probe.

FIG. 14 is graph showing a comparison of the DNA amplification by Rb69 components in an RPA reaction. Samples were analyzed using SYBR green dye.

FIG. 15 is a graph showing a comparison of the DNA amplification by Aeh1 components in an RPA reaction. Samples were analyzed using a fluorescent probe.

FIG. 16 is a graph showing a comparison of the DNA amplification by Aeh1 components and the effect of salt titration in an RPA reaction. Samples were analyzed using SYBR green dye.

FIG. 17 is graph showing a comparison of the kinetic behaviour of the Aeh1 system to the T4 system in an RPA reaction. Samples were analyzed using a fluorescent probe.

FIG. 18 is a graph showing Aeh1 UvsX and UvsY and heterologous gp32 can amplify DNA using an RPA reaction. Samples were analyzed using SYBR green dye.

FIG. 19 is a picture of an ethidium bromide stained agarose gel showing DNA amplification in an RPA reaction using heterologous reaction components: Rb69, gp32 and Aeh1 UvsX, and Aeh1 UvsY.

FIG. 20 is a schematic representation of novel Rb69 engineered constructs.

FIG. 21 is a schematic representation of additional novel Rb69 engineered constructs. The sequences, from top to bottom are SEQ ID NO:36, SEQ ID NO:37, SEQ ID NO:38, SEQ ID NO:39, SEQ ID NO:40, SEQ ID NO:41, and SEQ ID NO:42.

FIG. 22 is a graph showing a comparison of the kinetic behaviour of Rb69 and Rb69 H64S in an RPA reaction. Samples were analyzed using SYBR green dye.

FIG. 23 is a graph showing a comparison of the effects of Rb69 gp32 titration on RPA using wildtype Rb69 UvsX or mutant Rb69 UvsX H64S. Samples were analyzed using SYBR green dye.

FIG. 24 is a graph showing a comparison of the kinetic behaviour of mutant Rb69 H64S UvsX protein to wildtype Rb69 UvsX in an RPA reaction. Samples were analyzed using a fluorescent probe.

FIG. 25 is a graph showing mutant Rb69 H64S UvsX is functional in RPA over a range of Rb69 gp32 concentrations (300, 400, or 500 ng/μl of Rb69 gp32 protein). Samples were analyzed using a fluorescent probe.

FIG. 26 is a graph showing a titration of mutant Rb69 H64S UvsX in RPA (00, 150 or 200 ng/μl Rb69 H64S UvsX). Samples were analyzed using a fluorescent probe.

FIG. 27 is a graph showing additional titration of mutant Rb69 UvsX in RPA (60, 80 or 100 ng/μl Rb69 H64S UvsX). Samples were analyzed using a fluorescent probe.

FIG. 28 is graph showing the effectiveness of Rb69 gp32 in RPA reactions with T4 UvsX and UvsY. Samples were analyzed using a fluorescent probe.

FIG. 29 is a graph showing a comparison of the kinetic behaviour of T4 and the Rb69 UvsX/UvsY system in RPA when Rb69 gp32 is used at high concentrations. Samples were analyzed using a fluorescent probe.

FIG. 30 is a graph showing the kinetic behaviour of mutant Rb69 UvsX H64T in RPA. Samples were analyzed using a fluorescent probe.

FIG. 31 is a graph showing ATP titration when using Rb69 UvsX in RPA. Samples were analyzed using a fluorescent probe.

FIG. 32 is a graph showing the effect of T4 gp32 on Rb69 UvsX and UvsY in RPA. Samples were analyzed using a fluorescent probe.

FIG. 33 is a graph showing a comparison of the kinetic behaviour of mutant Rb69 UvsX constructs having modifications to the C-terminus, in an RPA reaction. Samples were analyzed using a fluorescent probe.

FIG. 34 is a graph showing a comparison of the kinetic behaviour of additional mutant Rb69 UvsX constructs having modifications to the C-terminus, in an RPA reaction. Samples were analyzed using a fluorescent probe.

FIG. 35 is a graph showing the titration of PEG 35,000 when using mutant Rb69 UvsX H64S 2xLDE in an RPA reaction. Samples were analyzed using a fluorescent probe.

FIG. 36 is a schematic of novel, engineered, hybrid UvsY constructs.

FIG. 37 is a graph showing the kinetic behaviour of novel UvsY hybrid constructs with T4 UvsX and T4 gp32 in RPA. Samples were analyzed using a fluorescent probe.

FIG. 38 is a graph showing a comparison of novel UvsY hybrid constructs with Rb69 UvsX and Rb69 UvsY in RPA.

FIG. 39 is a graph showing the kinetic behaviour of mutant Rb69 UvsX H64S/T6-1 2xLDE in RPA. Samples were analyzed using a fluorescent probe.

FIG. 40 is a graph showing the titration of Rb69 gp32 in the presence of mutant Rb69 UvsX H64S/2xLDE in RPA. Samples were analyzed using a fluorescent probe.

FIG. 41 is a graph showing the kinetic behaviour of mutant Rb69 UvsX H64S/2xLDE and Rb69 H64S/F69M/G70S/T6-1/2xLDE in RPA. Samples were analyzed using a fluorescent probe.

FIG. 42 is a graph showing the kinetic behaviour of mutant Rb69 H64S T68S/L68N/T4/2xLDE in RPA. Samples were analyzed using a fluorescent probe.

FIG. 43 is a graph showing the effect of titration of Rb69 gp32 when using mutant Rb69 UvsX H64S T67S/L68N/T4/2xLDE in RPA. Samples were analyzed using a fluorescent probe.

FIG. 44 is a graph showing the activity of mutant Rb69 UvsX H64S/T67S/L68N T4 2xLDE protein with T4 gp32 in RPA. Samples were analyzed using a fluorescent probe.

FIG. 45 is a graph showing the activity of Rb69 UvsX chimeras containing DNA-binding loops from phage 133, cyanophage, and Aeh1 in RPA. Samples were analyzed using a fluorescent probe.

FIG. 46 is a graph showing the activity of mutant Rb69 UvsX H64S T6 2xLDE in RPA. Samples were analyzed using a fluorescent probe.

FIG. 47 is a picture of an ethidium bromide stained gel showing amplified DNA products from RPA reactions using 0.1 mM, 0.5 mM, 1 mM, 2 mM, 3 mM manganese.

FIG. 48 is a graph showing DNA amplification using S. Aureus Pol I in RPA. Samples were analyzed using SYBR green dye.

FIG. 49 is graph showing heparin the onset of noise detection using water as a control in RPA reactions. Samples were analyzed using SYBR green dye.

FIG. 50 is a graph showing improved resolution of low copy target numbers by the use of Heparin in RPA reactions. Samples were analyzed using a fluorescent probe.

FIG. 51 is graph showing DNA amplification using blocked primers in RPA. Samples were analyzed using a fluorescent probe.

FIG. 52 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX and Rb69 gp32 in the presence or absence of UvsY loading agent.

FIG. 53 is another picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX and Rb69 gp32 in the presence or absence of UvsY loading agent.

FIG. 54 is a picture of an ethidium bromide stained agarose gel showing DNA amplification of small genomic DNA targets using T6 H66S UvsX and Rb69 gp32 in the presence or absence of UvsY loading agent.

FIG. 55 is a picture of an ethidium bromide stained agarose gel showing DNA amplification of complex genomic DNA targets using T6 H66S UvsX and Rb69 gp32 in the presence or absence of UvsY loading agent.

FIG. 56, is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX and Rb69 gp32 in the presence or absence of UvsY loading agent and in the presence or absence of PEG.

FIG. 57 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX with T4 gp32 or Rb69 gp32 in the presence or absence of UvsY loading agent.

FIG. 58 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX with Rb69 gp32 or Aeh1 gp32 in the presence or absence of UvsY loading agent.

FIG. 59 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX or T4 UvsX with Rb69 gp32 in the presence or absence of UvsY loading agent.

FIG. 60 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX or T4 UvsX with T4 gp32 in the presence or absence of UvsY loading agent.

FIG. 61 is a graph showing DNA amplification using T4 UvsX or T6 H66S UvsX with Rb69 gp32, in the presence of absence of UvsY loading agent. Samples were analyzed using a fluorescent probe system.

FIG. 62 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 UvsX or T6 H66S UvsX with Rb69 gp32 in the presence of absence of UvsY loading agent.

FIG. 63 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX or Rb69 UvsX with Rb69 gp32 in the presence of absence of UvsY loading agent.

FIG. 64 is a picture of an ethidium bromide stained agarose gel showing RPA products using Rb69 UvsX or Aeh1 UvsX with Rb69 gp32 in the presence or absence of UvsY loading agent.

FIG. 65 is a picture of an ethidium bromide stained agarose gel showing RPA products using T6 H66S UvsX or Rb69T6loop2H64S UvsX with Rb69 gp32 in the presence or absence of UvsY loading agent.

FIG. 66 is graph showing the results of the effects of titrating Rb69 gp32 in an assay designed to detect gp32 activity. Samples were analyzed using a fluorescent probe.

FIG. 67A-67C are graphs comparing the activity of T4, Aeh1 and Rb69 gp32 molecules in an assay designed to detect gp32 activity. Samples were analyzed using a fluorescent probe.

FIGS. 68A-68C are graphs comparing the upper temperature limits of T4, Aeh1 and Rb69 gp32 molecules in an assay designed to detect gp32 activity. Samples were analyzed using a fluorescent probe.

FIG. 69 is a graph showing the comparison of DNA amplification in RPA reactions using T4 UvsX with Rb69 gp32, in the presence and absence of UvsY loading agent. Samples were analyzed using a fluorescent probe.

FIG. 70 is an additional graph showing the comparison of DNA amplification in RPA reactions using T4 UvsX with Rb69 gp32, in the presence and absence of UvsY loading agent. Samples were analyzed using a fluorescent probe.

FIG. 71 is a picture of an ethidium bromide stained agarose gel showing RPA products using T4 UvsX and Rb69 gp32 in the presence or absence of UvsY loading agent.

DETAILED DESCRIPTION OF THE INVENTION

This invention constitutes novel enabling data on the use of diverse, hybrid and engineered recombinase enzymes. The utility of a variety of recA/UvsX-like recombination proteins and associated recombination factors for carrying out RPA reactions is shown.

Surprisingly, it was discovered that variant recombinases (e.g., novel engineered chimeric and mutant recombinases) and their associated components display differences in kinetics, differences in optimal PEG concentrations and SSB concentrations, and differences in dependence on recombinase loading factors. Furthermore, the novel chimeric and mutant proteins of the invention have permitted the elucidation of specific peptide regions that profoundly influence these behaviours.

The origin of some of the observed variation, and location of some key amino acids residues influencing activities in RPA assays is described herein. Particularly important are a mobile DNA-binding loop, as well residues in the Walker A motif found in ATPases. Notably it was discovered that the peptide corresponding to DNA binding loop 2 in E. coli RecA is very important, and that this peptide is generally unrelated to E. coli RecA, and quite variant among RecA/UvsX-like proteins from the myoviridae. Surprisingly, it was discovered that the T6 UvsX protein, and derivatives of it, display very significant UvsY-independent activity in RPA reactions. This UvsY-independent activity may also be extended to other UvsX species under conditions which particularly favour UvsX-loading but is most obvious for T6 and its derivatives. This analysis has permitted the engineering of altered T6 and Rb69 UvsX recombinase proteins for use in RPA, and has set the stage for further optimization and the development of engineered super-recombinases for the RPA system. Surprisingly, T6-derived recombinases show only partial requirement for loading proteins, albeit loading proteins improve reaction performance and robustness. Hybrid proteins can be utilized which display altered activities in the RPA process. Systems comprising heterologous combinations of recombination components may also be effectively used.

Additional components and conditions to improve RPA reactions are also provided herein. For example, the present invention provides other crowding agents which impart similar or even greater effects than Carbowax 20M (PEG compound) on RPA reactions. The inclusion of crowding agents, in particular those having a molecular weight of at least 10,000 and less than 100,000 was found to be highly stimulatory in RPA reactions. Such crowding agents include but are not limited to polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polystyrene, Ficoll, dextran, PVP, and albumin. In particular, PEG molecular weight 35,000 was found to be very effective in RPA reactions. The present invention also provides the use of heparin in RPA reactions, as an agent to reduce the level of non-specific primer noise, and the ability of E. coli exonuclease III or E. Coli exonuclease IV to rapidly polish 3′ blocking groups or terminal residues from recombination intermediates. Additionally, manganese ions are shown to be able to replace Magnesium, but at much lower concentrations.

Further, the present invention provides the use alternative polymerases capable of strand displacement synthesis for use in RPA reactions, including repair class polymerases, and polymerases which lack proof-reading activity. Surprisingly, the large fragment, not the full protein, of bacterial polymerase I repair enzymes which bear homology to the Pol I class of E. coli, Bacillus subtilis, and Staphylococcus aureus were found to be effective in RPA reactions, thus extending the repertoire of polymerases shown to be effective and further supporting the view that repair class, strand-displacing, polymerases from prokaryotes (and possibly phage) are generally effective.

Brief Description of RPA

RPA is a method (process) for amplifying DNA fragments. RPA employs enzymes, known as recombinases, that are capable of pairing oligonucleotide primers with homologous sequence in duplex DNA. In this way, DNA synthesis is directed to defined points in a sample DNA. Using two gene-specific primers, an exponential amplification reaction is initiated if the target sequence is present. The reaction progresses rapidly and results in specific amplification from just a few target copies to detectable levels within as little as 20-40 minutes.

RPA reactions contain a blend of proteins and other factors that are required to support both the activity of the recombination element of the system, as well as those which support DNA synthesis from the 3′ ends of olignucleotides paired to complementary substrates. The key protein component of the recombination system is the recombinase itself, which may originate from prokaryotic, viral or eukaryotic origin. Additionally, however, there is a requirement for single-stranded DNA binding proteins to stabilize nucleic acids during the various exchange transactions that are ongoing in the reaction. A polymerase with strand-displacing character is requires specifically as many substrates are still partially duplex in character. Reduction to practice has established that in order to make the reaction capable of amplifying from trace levels of nucleic acids precise in vitro conditions are required that include the use of crowding agents and loading proteins. An effective system comprising bacteriophage T4 UvsX recombinase, bacteriophage T4 UvsY loading agent, bacteriophage T4 gp32 and Bacillus subtilis polymerase I large fragment has been reported earlier.

Analysis of Key Residues and Engineering Novel Recombinase Proteins

In an effort to learn more about the optimal conditions and proteins for performing RPA reactions efforts to clone and produce RecA/UvsX-like proteins from the myoviridae bacteriophages which are relatives of the T4 bacteriophage were made. Additionally other key protein components were identified, which might be required for RPA reactions from each respective phage, e.g., equivalents to the gp32 protein and the UvsY protein. FIG. 1 shows a schematic representation of clones used to generate variant UvsX, UvsY and gp32 proteins. Hexahistidine tags were engineered at the N or C termini via incorporation of extra bases in oligonucleotides into PCR amplification primers used in their cloning. Templates were genomic phage DNA. T6 was obtained from the DSMZ stock centre in Germany, while Rb69, Aeh1 and KVP40 phages were obtained from the Institute Felix D'herelle in Canada.

A comparison of the biological activity of these proteins and analysis of the relationship of any biochemical differences to variation in the amino acids sequence of these proteins was made. Although none of the bacteriophage UvsX or UvsY proteins have been crystallized (or are unavailable in public databases, UvsX proteins are close relatives of bacterial RecA proteins for whom the structure is known. It has been hypothesized that RecA and UvsX originated from a common ancestor (Story et al., 1993). Although RecA and UvsX proteins share only weak homology at the primary sequence level, they show very similar geometries and pitches when assembled onto DNA and share blocks of homology comprising the potential subunit interfaces. They also share other features associated with bacterial RecA proteins such as acidic C-terminal residues likely involved in modulating DNA affinity on duplex and single-stranded DNA (Benedict and Kowalczykowski, 1988). As described herein, UvsX proteins were modeled onto the known RecA protein sequence using a standard primary protein sequence alignment as template. This allowed the effects of primary peptide sequence variation to structural position and known biological function of regions involved in DNA binding, ATP binding and hydrolysis, subunit interface, etc., to be observed.

RecA and T4 UvsX

FIGS. 2 and 3 show a primary sequence alignment of bacteriophage T4 UvsX with E. coli RecA, and a representative 3-D structure of a model of an active E. coli RecA filament. These two proteins share 23% identity and are 43% similar at the primary sequence level. Various key regions of the RecA molecule which are implicated in biological activity and relevant to the discussion here are indicated on the alignment and the structure. The regions involved in binding and hydrolysing nucleotides are found intimately associated with the face of the protein involved in contacting the DNA backbone. Note that key residues defining the so-called Walker A motif (found in all ATP-hydrolysing enzymes) are found in both proteins. The Walker A consensus is often stated as A/G XXXXGK S/T (SEQ ID NO:43), where X is any amino acid (Walker et al., 1982). The E. coli RecA protein Walker A motif perfectly matches this consensus, while T4 UvsX notably lacks the second glycine immediately preceding the lysine. Most phage UvsX proteins other than T4 also lack this second glycine (see FIG. 5), having a phenylalanine instead, however this is not the case for the somewhat more divergent recombinases of cyanophages SSM2 and SSM4. These latter proteins do possess the second glycine, and on the whole significantly more closely resemble RecA with regard to the Walker A sequence.

Other peptide sequences of interest for later discussions include those regions described as DNA binding loops 1 and 2 in E. coli RecA. These loops have been described as highly mobile, are implicated in direct contacts to DNA (Malkov and Camerini-Otero, 1995), and also as participating in the nucleotide hydrolysis process (Voloshin et al., 2000). It is thus significant to note that both the DNA binding loops (disordered in some crystal structures), and the Walker A motif are all located in close proximity to one another on a common face of the protein. One can readily imagine that the dependence of ATP interaction for DNA binding, and the concomitant stimulation of ATP hydrolysis caused by DNA binding, are intimately interdependent processes involving direct interactions between these various peptides, ATP and DNA.

A last region of interest is the very C terminus of the E. coli RecA and T4 UvsX proteins. In both cases there is an acidic peptide sequence. This has previously been shown to influence the DNA binding properties of E. coli RecA, in particular when removed promoting stronger binding to double-stranded DNA and a reduction in dependence in magnesium ions and various salt and pH conditions (Eggler et al. 2003; Lusetti et al. 2003). Notably removal of this acidic sequence may decrease the frequency with which disassembly of recombinase filaments occurs. In earlier work, it was reported that removal of this acidic sequence from either RecA or T4 UvsX altered the activity of the proteins in RPA reactions having a generally detrimental effect which may result from undesirably high DNA affinity on duplex substrates (Piepenburg et al. U.S. Ser. No. 10/931,916).

T4 vs T6 UvsX Protein An Unexpected Number of Amino Acid Substitutions

A number of UvsX-like protein molecules are aligned in FIG. 5. The T6 UvsX protein was cloned, sequenced, and expressed in E. coli with a histidine tag sequence at the C terminus. A similar draft sequence of the T6 UvsX protein was discovered in a database provided at Tulane University. A surprising discovery was that quite a number of amino acid residues were variant between T4 and T6 UvsX proteins. There were 38 substitutions between the two proteins and a 2 amino acid insertion at the N-terminus. The reason that this significant level of heterology was a surprise is that T2, T4, and T6 (the so-called T-even phages) are regarded as fairly close relatives of one another. Oddly, all the substituted amino acid residues were confined to more- or -less the N-terminal half of the protein, while the C-terminal half was completely conserved. This seemed particularly odd because when UvsX relatives from more diverged myoviridae members were studied it was noted that other regions such as the last C-terminal 30-40 residues were the least conserved. It was also noted that the primary DNA sequence was fairly well-conserved in the coding sequence for the C-terminal half of the protein with few base changes even on wobble positions, while the N-terminal half showed concentrated clusters of base changes. Indeed many of the substituted amino acids required 2 base changes to achieve the amino acid substitutions observed. As described below, some of these substitutions have occurred in regions important for function of the recombinase, and it is proposed that rather than supporting a model of mutations occurring principally at silent positions, in this case many substitutions may have been selected due to conferring measurable biochemical variation to the polypeptide.

Relative Activity of T4 and T6 UvsX Proteins

The activity of the T6 UvsX protein in DNA amplification assays was tested and monitored in real-time with a fluorescent probe or minor-groove binding dye, as well as some experiments in which products at end-point were monitored on agarose gels. In these experiments gp32 and UvsY proteins from T4 were employed. This approach was taken as the gp32 and UvsY proteins from T4 and T6 appeared very similar. T6 UvsY was sequenced and only 2 highly conservative substitutions were found (see FIG. 4). T6 gp32 had only 4 substitutions, and a single amino acid insertion. It was determined that the T6 UvsX protein was indeed active and worked effectively to amplify targets in this heterologous system. When assayed on agarose gels there was no significant consistent differences between reactions performed with T4 and T6 UvsX proteins (90 minute reactions) (small differences in final product accumulation were observed here, but were not consistent and may arise through pipetting inaccuracies) (see FIG. 8). However, when assayed in real-time using SYBR-green or with a probe-based approach, a measurable difference in reaction kinetics was observed. Reactions performed with T6 UvsX were consistently shallower in the curve of signal accumulation than those performed with T4 UvsX, although generally the time at which the signal threshold was crossed were similar (see FIGS. 9 and 10 showing comparison of T4 and T6 UvsX amplification kinetics using SYBR-green or a probe). Without intending to be bound by any theory, the reproducibility of this effect appears to have been underpinned by real biochemical differences between these 2 proteins. Note here however that one concern should be raised about the interpretation of experiments performed with a probe-based system. In order to generate strong signals in probe-based experiments, an asymmetric ratio of amplification primers were employed to encourage an excess of single-stranded DNA complementary to the probe late in the reaction. Should variant recombinases influence the ability of this single-stranded DNA to interact with the probe then it may mask signals generated in this system and lead to lower overall fluorescence. This effect could have a mechanistically different origin to a similar response caused by poorer overall amplification. In either case, however, it would reflect biochemical differences in the amplification components.

Source of Variability Between T4 and T6 UvsX Walker A Motif

In an effort to understand a possible relationship between the differing primary amino acid sequences of T4 and T6 UvsX and the observed biochemical differences the known structural and functional information available for RecA was studied, and the information was translated to the phage proteins. Of particular interest were the regions potentially involved in DNA binding and nucleotide hydrolysis. As discussed earlier, the affinity of recombinases for ssDNA and dsDNA, and their turnover rates which are related to ATP hydrolysis rate, are factors likely to critically affect the behaviour of RPA reactions. Thus, the sequence of, and surrounding, the so-called Walker A motif (or ‘P-loop’) (consensus normally described as A/G XXXXGK S/T (SEQ ID NO:43)) which is highly conserved among most known (non-cyanophage) UvsX-like proteins, but is slightly eccentric in that it lacks the second glycine of the canonical Walker A motif (see FIG. 5, sequence GPSKHFKS (SEQ ID NO:44) in most proteins and APSKHFKT (SEQ ID NO:45) in Rb69), and is slightly different in T4 UvsX (GPSKSHFKS(SEQ ID NO:46))) was of particular interest. This motif is implicated in the binding and hydrolysis of ATP, possessing residues involved in co-ordinating the triphosphate backbone, and polar residues implicated in stimulating hydrolysis. T4 UvsX possesses a serine residue at position 64 which is a histidine in all other UvsX proteins except the distant cyanophage homologs (which have a P-loop more reminiscent of RecA proteins). It was noted that this novel arrangement resulted in the generation of a new lysine-serine dipeptide in the middle of the Walker A motif, a feature normally found only at the C-terminus of the motif, and hence a re-iteration. Crucially the lysine and serine (or threonine) residues of the Walker A motif are key to the co-ordination of the gamma phosphate (lysine) and hydrolysis of the phosphate-phosphate bond (serine/threonine). It was known from early studies that T4 UvsX demonstrated the unusual property that the protein hydrolysed ATP to AMP and pyrophosphate, as well as to ADP and phosphate, the more traditional reaction (Formosa and Alberts, 1986). This raised the question whether this catalytic plasticity was imparted by this central lysine-serine dipeptide which could perhaps co-ordinate the beta-phosphate and catalyse hydrolysis of the alpha-beta phosphate-phosphate bond in a manner equivalent to the more traditional reaction (analysis of the RecA protein structure suggested that these central residues might be appropriately positioned, see FIG. 3). If true then it was anticipated that non-T4 UvsX proteins would not generate AMP and pyrophosphate, and this could have significant implications on their relative behaviours in RPA reactions. For example, in T4 UvsX, this activity might increase the overall total ATP hydrolysis activity with implications for the degree of dynamicity of the recombinase in the reaction. Also, as ATP and ADP are reported to be associated with different nucleoprotein helical pitches (Ellouze et al., 1995), so AMP might promote yet a third pitch which could be significant. Thus, this variant residue might underpin some or all of the variation observed between T4 and T6 UvsX.

Mutant T6 proteins were generated in which the histidine residue was replaced with serine at the equivalent central Walker A motif position as found in T4. This resulted in a protein which appeared improved relative to the original T6 protein sequence. In a variety of experiments involving sensing product accumulation in real-time, the slope was steeper and maximal signal generated was higher for the mutant T6 protein (FIG. 12). It was concluded that this mutation directly benefits the behaviour of RPA reactions, particularly late in the reaction. This may result from one or more of several sources; (i) The recombinase may less efficiently bind duplex DNA, thus suffering less from out-titration of recombinase by product, (ii) The recombinase may hydrolyse ATP more effectively on duplex DNA, thus recycling more efficiently from duplex DNA, (iii) the hydrolysis the generate AMP and PPi from ATP may be associated with a new nucleoprotein pitch which is useful for maintaining high dynamic activity late in the reaction. Other explanations are, of course, possible.

Residues C Terminal to Walker A Motif

Despite significant improvement in the activity of T6 UvsX once histidine 66 had been mutated to serine, the protein still seemed to remain slightly different in behaviour to the T4 UvsX. Thus, other amino acids were examined. As mentioned earlier, the 38 amino acid substitutions between T6 and T4 are clustered in the N-terminal half of the protein. Substitutions were found in several places that might be influential, namely residues directly C-terminal to the Walker A motif as well as those in the putative mobile DNA-binding loops (see more below). FIG. 5 shows that T6 has 2 amino acids directly after the Walker A motif, namely methionine 71 and serine 72, that are different to T4 in which these residues are phenylalanine and glycine. In FIG. 3, Panel B, the putative position of the T4 residues phenylalanine (F69) and glycine (G70) are indicated (assuming similar positioning in T4 UvsX as in E. coli RecA). Note that they are very close to the other important residues of the Walker A motif (or ‘P’ loop), and also to the putative mobile DNA binding loop2 whose beginning and end is indicated.

These variant residues were mutated in T6 UvsX to generate clone T6UvsX M71F/S72G the protein was made. This protein was tested in real-time assays and was found to be totally inactive (FIG. 13). It was concluded that one or both of these residues are non-substitutable in isolation and that they must have a biochemical interaction with other substituted residues which are also altered in T6 UvsX to compensate and allow correct folding and/or activity. Further evidence that one or both of these residues confer measurable interaction with some other peptide regions is suggested by data presented later analysing Rb69 chimeras. In summary these two residues (M71 and S72), at least in isolation, are not silent substitutions between T4 and T6, nor do they in isolation appear responsible for conferring the slight difference between T4 and T6 UvsX.

DNA Binding Loop 1

Comparison of T4 and T6 peptide sequences suggested that those sequences likely comprising the equivalent of DNA binding loop 1 of E. coli RecA were generally very highly conserved between T4 and T6 UvsX (FIG. 5). Nonetheless, 2 residues at the end of the putative region were variant, namely serine 164 of T6 which is valine in T4, and alanine 166 of T6 which is serine in T4. These residues were both mutated together in T6 to generate the clone T6 UvsX S164V/A166S. This protein was expressed, purified, and tested it in real-time assays. The first experiment performed with this protein is shown in FIG. 13, in which it performs well, and slightly better than wild type T6. It was noted that in later experiments its behaviour seemed almost indistinguishable from wild type T6. Consequently, within the boundaries of error of the experiments, it is suggested that these substitutions are silent between T4 and T6 polypeptides and do not contribute significantly to the assayable characteristics addressed in these experiments.

DNA Binding Loop 2

One of the most interesting peptide sequences in E. coli RecA is the so-called mobile DNA binding loop 2. This peptide has been shown to possess DNA binding activity, even in complete isolation from the whole protein (Voloshin et al., 1996). The loop has also been variously implicated in stimulating ATP hydrolysis when recombinase is bound to DNA, and even to have a catalytic role in ATP hydrolysis (Voloshin et al., 2000). It was anticipated that the equivalent sequence would be of great importance to UvsX function. Note however that this peptide is unrelated to the RecA peptide.

As illustrated in FIG. 5, T6 and T4 have 3 substitutions in the region of the putative DNA binding loop 2 region. An additional alignment of all known UvsX-like proteins in this region is shown below. Sequences have been loosely grouped by similarity. An alignment of the RecA loop is shown in this region also.

DNA binding loop 2 sequences T6 NHT 

ET

EMFSKT VMT GG (SEQ ID NO: 47) RB3 NHT 

ET

EMFSKT VMT GG (SEQ ID NO: 48) LZ2 NHT 

ET

EMFSKT VMT GG (SEQ ID NO: 49) RB14 NHT 

ET

EMFSKT VMT GG (SEQ ID NO: 50) RB32 NHT 

ET

EMFSKT VMT GG (SEQ ID NO: 51) 133 NHT 

QTLEMFSK

 VMT GG (SEQ ID NO: 52) T4 NHT YETQEMFSKT VMG GG (SEQ ID NO: 53) AE65 NHT YETQEYFSKT VMS GG (SEQ ID NO: 54) PHI 1 NHT YETQEMFSKT VMS GG (SEQ ID NO: 55) RB49 NHT YETQEMFSKT VMS GG (SEQ ID NO: 56) RB16

HT Y

TQEM

SK

 VIS GG (SEQ ID NO: 57) RB43

HT Y

TQEM

SK

 VIS GG (SEQ ID NO: 58) AEH1

HT Y

TQEM

SK

 VVS GG (SEQ ID NO: 59) KVP40 NHT YQTQEI

SKT VMS GG (SEQ ID NO: 60) NT1 NHT YQTQEM

SKT VMS GG (SEQ ID NO: 61) PSSM2 NHT Y

IGS

VPTK EMG GG (SEQ ID NO: 62) PSSM4 NHT Y

GA

IPTK EMG GG (SEQ ID NO: 63) SPM2 NHT Y

GS

VPTK EMG GG (SEQ ID NO: 64) RB69 NHT A

E

GLYPKE IMG GG (SEQ ID NO: 65) JS98 NHT A

E

G

YPKE IMG GG (SEQ ID NO: 66) RECA QI R

K

V

FGNPETTT GG (SEQ ID NO: 67) Required RecA **  * *        * * ** Hydrolysis  ∘  ∘ ∘          ∘ Involvement

It was noted that residue isoleucine 199 and isoleucine 202 were not only different in T6 (being respectively a tyrosine and glutamine in T4 UvsX), but were T4-like in many of the loops from other UvsX relatives. This latter observation suggested that they might not be trivially substituted. Furthermore it was noted that using the best possible alignment generated with the RecA loop, isoleucine 199 corresponded to a RecA residue shown to be necessary for activity. The consequence of altering either 1199 or 1202 to the T4 equivalents was investigated. Mutant clones were generated and the proteins were expressed. Substitution of either 1199 or 1202 to their T4 equivalents completely inactivated the protein. This result was something of a surprise, but once again highlights the fact that these substitutions are not silent and have significant biological consequences. It was assumed that each of these substitutions in T6 UvsX is matched by at least one other compensating substitution elsewhere. Furthermore, all UvsX molecules with a loop length similar to T4 and T6 (see below) possess a tyrosine and glutamine like T4 at these positions apart from those in the T6 group and phage 133, and in these cases both residues are altered to either isoleucine (T6 group) or leucine (133). It was hypothesized that these particular residues have key interactions with one another and must be substituted in unison. To test this hypothesis, a double mutant T6 UvsX molecule was generated with both of these residues changed to the T4 equivalents. It was found that the double mutant protein also failed to demonstrate activity in amplification assays suggesting that other variant residues which are substituted between T4 and T6 underpin the substitution compatibility problem. This highlights the fact that a number of the substitutions between T4 and T6 UvsX proteins occur in non-silent positions and have real influence on protein biochemistry.

Amplification Systems Employing Rb69, Aeh1 and KVP40 Proteins

Clones encoding the UvsX, UvsY and Gp32 proteins of bacteriophages Rb69, Aeh1 and KVP40 were generated, as indicated in FIG. 1. Alignments of these 3 proteins are shown in FIGS. 5, 6, and 7 and include other known homologs. A possible error in the NCBI Genbank database was noted with regard to the Rb69 UvsY sequence. According to the database the Rb69 UvsY would have an N-terminal extension relative to the sequence shown here, however attempts to express this longer polypeptide were unsuccessful and lead to the re-examination of the sequence. It was noted that all other identifiable UvsY proteins begin at a near-identical point and that the database entry included a methionine at the equivalent position to the first methionine of the others. It was deduced that the automatic annotation software was erroneous. Probable errors in annotation were also identified for some of the cyanophage entries for UvsY and Gp32 which had been artificially truncated at the N terminus compared to the sequences shown in the alignments herein.

All of the proteins illustrated in FIG. 1 expressed and purified robustly with the exception of KVP40 gp32. Only relatively limited amounts of this protein were recovered despite no apparent errors in the sequence of the clone. A possible source of this biochemical oddity was speculated. Study of the alignment of gp32 molecules shown in FIG. 7 reveals that KVP40 is eccentric relative to T4, T6, Rb69, and Aeh1 gp32 molecules in the part of the primary sequence corresponding to residues implicated in co-ordinating Zinc atoms in T4 gp32. More specifically 4 residues have been implicated to be involved in binding zinc in T4 gp32, these are either histidine 64, cysteine 77, cysteine 87, and cysteine 90 (Qiu and Giedroc D. P., 1994) or Histidine 81 cysteine 77, cysteine 87, and cysteine 90 which were reported earlier (Giedroc et al., 1987). In T4, T6, Rb69, and Aeh1 gp32's these 4 residues are highly conserved with identical spacings and very high conservation of residues in general between histidine 64 and cysteine 90.

Zinc co-ordination has been shown to be critical for the cooperative behavior of T4 gp32 (Nadler et al., 1990), and the apoprotein does not support effective RPA reactions (see Piepenburg et al.). However KVP40 gp32 has significant disruption to the spacing of putative coordinating residues in the C-terminal half of this region, and little or no homology with other residues in T4, T6, RB69, and Aeh1 in this region. It was proposed that this disruption has altered the metal-binding properties of KVP40 gp32 relative to T4, T6, Rb69 etc. Without intending to be bound by any theory, it is possible that KVP40 no longer binds Zinc, or instead uses another metal atom such as Cobalt. It was noted that KVP40, a broad spectrum vibriophage, was isolated from a marine environment in which trace metal conditions may be different to those inhabited by coliphages. Without intending to be bound by any theory, perhaps an altered metal dependency and folding characteristics have influenced the efficiency of expression in E. coli. Furthermore it was noted that the cyanophage SSM2 and SSM4 putative protein sequences are conspicuous in the absence of any of the conserved coordinating cysteine residues. It was assumed that these gp32 molecules do not contain a zinc, or similar, metal atom. This is of some considerable interest as occasional problems in the activity of gp32 have been encountered, likely caused by co-purification of apoprotein, or by loss of zinc from the protein under poor storage conditions. Furthermore as gp32 loses the zinc atom when heat denatured, it has consequently has been of limited use in PCR or other techniques requiring a heat denaturation step. If the SSM2 and SSM4 gp32 proteins have engineered a way to have similar co-operative behavior without zinc atoms, and still have all the other properties required for RPA, then they could be very useful agents for RPA or other techniques.

RPA with Rb69 Proteins

RPA reactions were configured with Rb69 UvsX, Rb69 UvsY, and Rb69 gp32. Limited investigation into optimal component concentrations established that reaction behavior was notably distinct from T4 or T6 UvsX-based systems. It was found that higher quantities of UvsY were required for optimal activity. FIG. 14 shows amplifications performed with SYBR green and FIG. 24 shows reactions monitored with a fluorescent probe system. Reactions work well but have slightly slower kinetics than T4 or T6 based reactions. Oddities in the behavior of the Rb69 amplification system were noted. For example the amplification system was strangely very sensitive to overtitration of both Rb69 gp32 (see FIG. 23), and sensitive to overtitration of Rb69 UvsX (see FIGS. 26 and 27). Both these sensitivities were distinctive and different from observations made with T4 (and T6) amplification systems. Significant efforts were made to address the underlying source of these differences which are later described. However, it was noted that despite these variations, highly effective RPA reactions may be configured with Rb69 components, again confirming the generality of the RPA system and the possibility of using a wide range of recombinase agents and associated factors.

RPA with Aeh1 Proteins

RPA reactions were configured with Aeh1 UvsX, Aeh1 UvsY, and Aeh1 gp32 (see FIGS. 15, 16, and 17). As with the Rb69 system it was found that the Aeh1 system was clearly functional, but showed differences to the T4 and T6 based systems. There appeared to be dependency on higher quantities of polyethylene glycol, and once again kinetics tended to be somewhat slower than observed with T4 and T6.

One observation that was made using both gel-based assays (FIG. 19) and real-time assays (FIG. 18) is that an amplification system could be configured that used Rb69 gp32 in combination with Aeh1 UvsX and Aeh UvsY, albeit perhaps not as robust as when all Aeh1 components are used. This interesting result suggests that the gp32 species used may not absolutely need to match the UvsX and UvsY species.

RPA with KVP40 Proteins

KVP40 gp32 did not express robustly in E. coli under the conditions of growth and induction used. Consequently an amplification system using KVP40 components was unable to be established. Nevertheless there is some reason to believe that KVP40 UvsX and UvsY may possess basic biochemical activities required for establishing RPA reactions. In one experiment KVP40 UvsX and UvsY were combined with either gp32 from Rb69, or gp32 from Aeh1. Under these conditions there was evidence of DNA synthesis and while a product of expected size was not generated the presence of apparently amplified primer artifacts lends support to the idea that recombination-mediated polymerase priming was occurring. This suggests partial functionality of this heterologous systems, and it is proposed that KVP40 might also in principle be adapted to a useful RPA system.

Rb69 Chimeras

The source of some of the most marked differences in RPA reactions using Rb69 components rather than those of T4 and T6 are addressed herein. FIG. 14 reveals one of the first oddities of the Rb69 system, namely that Rb69 seems to require more UvsY than the T4 or T6 systems. A second oddity is that the Rb69 system is very sensitive to the concentration of gp32 that is employed as revealed in FIG. 23. Such a high degree of sensitivity was not noted for the T4 system. A third oddity is that the Rb69 RPA system is very sensitive to the concentration of UvsX employed as revealed in FIGS. 26 and 27, in particular suffering if excess protein is employed. Other peculiarities were discovered in addition to these as protein in heterologous mixtures were compared with other proteins. For example it was found that Rb69 UvsX could not tolerate T4 gp32 at all, while Rb69 gp32 worked very efficiently with T4 UvsX and T4 UvsY (FIGS. 28, 29, and 32). Similarly it was found that Rb69 UvsY would readily support amplification with heterologous T4 components (FIG. 37), but when Rb69 UvsX was employed the type of UvsY used had a significant impact on the outcome of the experiment (FIG. 38). Rb69 UvsY gave the highest stimulation, while T4 UvsY or hybrids between T4 and Rb69 UvsY were markedly less effective.

A possible explanation to rationalize the above data is presented herein. Without intending to be bound by any theory, it is suggested that Rb69 UvsX is mainly responsible for the variant behavior of the Rb69 amplification system. Perhaps Rb69 UvsX has relatively poor DNA binding behavior in comparison with T4 UvsX, at least under the salt, pH, and other conditions employed by us here. As a consequence perhaps Rb69 UvsX has relative difficulty in coping with the excess quantities of gp32 present in the system, being a poor DNA-binding competitor, and, as such it is more dependant on highly effective UvsY behavior, is inhibited by excessive gp32, and sensitive to the fecundity of the gp32 and UvsY species employed which are presumably subtly different between Rb69 and T4 proteins (thus explaining why T4 UvsX is largely unaffected by the species of gp32 or UvsY used while Rb69 UvsX is affected).

This theory could account for most of the observations made about RPA reactions using RB69 components. However one aspect that is left unanswered by this is the question of why the reactions should be sensitive to overtitration of Rb69 UvsX, which on the face of it one would expect to help rather than hinder reaction kinetics. Without intending to be bound by any theory, perhaps a second factor that might be in play is that Rb69 UvsX may not support the hybridization of complementary oligonucleotides to one another. It is reported that RecA and UvsX support the hybridization of complementary oligonucleotides, a property essential to effective RPA reactions as strand displacement DNA synthesis must generate quantities of ssDNA that require conversion to duplex DNA via hybridization, not invasion, based priming. If true then the situation might be explained as follows: Rb69 UvsX has a low affinity for, or residence time on ssDNA, compared with T4/T6 UvsX which means that it competes poorly with excess gp32 (hence sensitivity to gp32 overtitration), however it also fails to support oligonucleotide hybridizations and thus encouraging overly high oligonucleotide-recombinase loading also leads to impaired amplification reactions as few primers are available for hybridization. Consequently a middle ground would have to be struck in which roughly half the primers are coated with UvsX and half are coated with gp32. That the maximal optimum RB69 UvsX concentration was found to be ˜100 ng/μl, which is roughly half that required to saturate all primers in the reaction may be no coincidence.

Despite the above ‘theory’ there exist other reasonable explanations, and other data exists that is somewhat inconsistent with this model. For example gel analysis of Rb69 component-mediated amplifications (not shown here) reveal larger amounts of product DNA than is typically generated found with a T4-based system. Overall such reactions gave the impression of extremely high recombinase activity somewhat inconsistent with the interpretation that Rb69 UvsX has weak DNA-binding behavior. This suggests that Rb69 UvsX might show altered ssDNA/dsDNA partitioning relative to T4 or T6 UvsX, perhaps showing less inhibition by duplex DNA build-up.

Whatever the rationale for the differences in behavior of Rb69 and T4/T6 UvsX molecules, which are speculative at this time, one peptide region that is prime suspect in all of this is the putative mobile DNA binding loop2. FIG. 5 showing the alignment of UvsX proteins reveals how very unusual the Rb69 loop2 sequence is compared to its nearest homologous neighbors. Unlike T4, T6, Aeh1, KVP40, phage 133 (and all UvsX molecules apart from JS98 which is a close Rb69 relative), and the cyanophage proteins, the Rb69 loop 2 has a different number of amino acids and appears completely recoded in comparison to the others. This is most unexpected, and given the attention paid to this loop in studies of RecA, and the results described above regarding subtle alterations found in the T4 and T6 loops, it was anticipated that this variant loop sequence might underpin much of the measurable differences.

Other putative UvsX-like loop2 sequences and Walker A amino acids were employed and used to replace the Rb69 version. Additionally, changes to the acidic C-terminus of the protein were investigated. FIGS. 20 and 21 show schematic representations of clones that were generated in order to express mutant proteins. These experiments followed a temporal flow of investigation which means that most data was generated by successive steps of alteration of clones which were generated in an Rb69 protein backbone.

Initially the histidine in the Walker A motif was substituted for serine as was done for T6. FIGS. 22 and 24 show experiments performed to compare Rb69 UvsX wild type with Rb69 H64S. FIGS. 22 and 24 show that Rb69 H64S performs better than the wild type equivalent. Samples were analyzed using either SYBR green or using a probe-based approach. This finding nicely mirrors the finding made with T6, and suggests that altering this histidine residue may be universally beneficial for UvsX proteins used for RPA. Second, the utility of altering the nature of the very C-terminus of the protein was investigated. It was noted (see FIG. 5) that Rb69 was very slightly shorter at the very C terminus relative to T6 and T4 UvsX. Examination of these proteins lead to the conclusion that the acidic residues found at the C terminus were loosely arranged in threes at the very protein terminus according to the rules (hydrophobic/structural)-(acidic)-(acidic). According to this model Rb69 was lacking one unit of this repeat relative to T4 and T6. It was hypothesized that the length of this acidic region would influence the RPA performance. To test this hypothesis, 2 novel clones with slightly extended the C-terminal Rb69 sequence were generated; in one case inserting the triplet of amino acids ‘LSD’ and in the second case inserting a tandem repeat of the triplet ‘LDE’ and thus 6 new residues (see FIG. 20). The proteins containing these alterations were tested in assays using a probe-based detection approach. Although not every experiment gave completely consistent results (possibly in part because different start copy numbers were used), in general a clear trend was noted. It was usually the case that the shape of the accumulation curve was slightly different between wild type Rb69. the ‘LSD’ mutant, and the ‘2xLDE’ mutant. The mutants generally showed a very slightly later onset of detection, but then had a slightly sharper signal accumulation incline, and a slightly higher final total fluorescence (FIGS. 33 and 34). Although the extent of this effect was somewhat variable between different experiments performed under slightly variable conditions, it was nonetheless sufficiently clear to conclude that these alterations had significant biological effect. Without intending to be bound by any theory, these alterations may slightly reduce the affinity/stability of recombinase for certain substrates, particularly perhaps duplex DNA, and as such alter the reaction kinetics with a particular emphasis on reducing the late phase reaction slowing that is precipitated by the accumulation of product.

The next steps were to investigate the DNA binding loop2 sequences which were suspected of underpinning much variation. The Rb69 loop2 sequence NHT AMEIGGLYPKE IMG GG (SEQ ID NO:68) was substituted for the T6 loop NHT IETIEMFSKT VMT GG (SEQ ID NO:69) except for the last variant threonine (bolded and underlined here) which was left as the native glycine found in Rb69. This was done because the T4 loop had a similar glycine to the Rb69 sequence, and assuming this residue was unimportant (or not strictly in the flexible loop region) it was left to avoid a more complex mutagenesis protocol. This new protein which had been generated in the backbone of the functional Rb69 H64S/2xLDE protein was tested. This protein was designated Rb69 H64S/T6-1/2xLDE in which T6-1 refers to the T6 DNA-binding loop2 lacking the last native threonine that precedes the pair of C-terminal glycines (see FIG. 20 and legend). This protein was found to have no activity in RPA assays (FIG. 39). It was speculated that this lack of activity might result from incompatibility between the DNA-binding loop and the residues in the nearby Walker motif Rb69 has an unusual Walker motif in several respects. First, it does not have a serine but rather a threonine as the main putative catalytic residue of the motif in contrast to the other non-cyanophage proteins. This threonine is followed by another atypical residue, leucine, which is also not found in other UvsX proteins. In addition to this the glycine found at the beginning of the Walker A consensus is an alanine in Rb69 UvsX unlike any other UvsX molecule (apart from the near-identical J598 protein) or even E. coli RecA.

In addition to the eccentric differences between Rb69 UvsX and other UvsX molecules, T6 UvsX also has eccentric residues in this region. In particular methionine 71 is not found in most other UvsX proteins except those that are near-identical to T6, or phage 133 (see FIG. 5). It was noted that phage 133 also had changes in the DNA-binding loop2 region (having leucines at the positions substituted to isoleucine in T6) which possibly represented evidence of a direct contact between these various residues. In all, the Rb69 Walker motif in its C-terminal region differs from T4 by 2 residues (compare Rb69 KTLFGL (SEQ ID NO:70) to T4 KSNFGL (SEQ ID NO:71)) and differs from T6 by 4 residues (compare Rb69 KTLFGL (SEQ ID NO:72) to KSNMSL (SEQ ID NO:73)). Changes in the Walker region in the backbone context of clone Rb69 H64S/2xLDE/T6-1 were generated making it like T4 (KSNFGL (SEQ ID NO:74)), like T6 (KSNMSL (SEQ ID NO:75)) or with changes made that are characteristic uniquely to T6 (KTLMSL (SEQ ID NO:76)). Attempts to express some of these clones failed despite the use of multiple sequenced clones apparently containing no errors. In fact it appeared that those clones that had been made equivalent to T4 or T6 sequences (KSNFGL (SEQ ID NO:77) or KSNMSL (SEQ ID NO:78)) would not express and purify properly. It was concluded that the ‘SN’ motif is not tolerated when the T6-1 DNA loop is inserted to replace the Rb69 DNA-binding loop2. This was most perplexing because this exchange is well-tolerated if the T4 DNA-binding loop 2 is used to replace Rb69, as later described. The one expressed clone (KTLMSL) appeared to have no activity in assays when tested.

A Complete T6 DNA-Binding Loop2 Sequence Demonstrates Activity

Clones were generated in which the last variant residue of the T6 DNA-binding loop 2 (NHT IETIEMFSKT VMT GG (SEQ ID NO:79)) in the chimeric Rb69-T6 constructs were restored. Clones corresponding to Rb69 H64S/2xLDE/T6-1/KSNMSL (SEQ ID NO:80) and Rb69 H64S/2xLDE/T6-1/wtRb69 Walker were generated but with the repaired threonine and thus designated Rb69 H64S/2xLDE/T6/KSNMSL (SEQ ID NO:81) and Rb69 H64S/2xLDE/T6/wtRb69 Walker. Once again, the clone with an altered Walker motif would not express and purify. Without intending to be bound by any theory, this implies close biochemical context between these Walker A residues and the variant isoleucines present in the T6 DNA-binding loop2. However, a surprising discovery was that the latter clone possessing only a repaired T6 DNA-binding loop and no alterations to the native Rb69 Walker A motif did express and proved to be functionally active (FIG. 46). Thus it appears that this last variant threonine residue is absolutely critical to the function of the T6 DNA-binding loop, at least when transferred to an Rb69 backbone. It was concluded that functional chimeric proteins may be generated, and that all of the three substitutions between T4 and T6 DNA-binding loop 2 sequences have measurable functional implications.

Rb69 Chimeras Containing T4 DNA-Binding Loop2 Sequences are Active

Further chimeric molecules containing the DNA-binding loop2 sequence of T4 UvsX were generated. In contrast to the Rb69/T6 chimeras these proteins were active regardless of whether the Walker motif was left unaltered in the native state or changed to be T4-like (KSNFGL (SEQ ID NO:82)) even though such a Walker A motif was not tolerated when the T6 DNA-binding loop was employed. Again it is stressed that this could reflect direct contacts between the ‘SN’ motif and the first few residues of the DNA-binding loop2. Some tendency of the protein made with a native Rb69 Walker motif to precipitate more readily from concentrated stocks was observed, which could indicate a slight incompatibility between heterologous sequences, but this was only a slight effect.

Improved Recombinase Behaviour for Rb69 Chimeras

From the above it may be concluded that DNA-binding loop 2 sequences may be exchanged between UvsX molecules from different origins to generate functional proteins in some cases. The Rb69 chimeric molecules generated were tested to determine whether they might display different characteristics to those exhibited by native Rb69. First, the protein was assayed to determine whether more resistant to overtitration of gp32 protein. FIG. 43 shows that the delay in signal onset that is measured when mutant protein containing a T4 DNA-binding loop is used is decreased when higher quantities of gp32 are used than is the case with native Rb69. It was concluded that the engineered design contributed some of the more tolerant activity found in T4 and T6 UvsX proteins to the Rb69 chimera. Next the protein was assayed to determine whether T4 gp32 could be employed to replace Rb69 gp32, something that had not been possible with the native Rb69 protein. It was found that indeed amplification reactions could now be carried out using Rb69 protein containing the T4 DNA-binding loop (see FIG. 44).

Thus it is possible to engineer UvsX proteins with novel biochemical activities by substituting key residues, and some of these are relatively improved compared to their native parents in RPA assays.

Other DNA-Binding Loop2 Sequences

To extend this analysis further and to its logical conclusion Rb69 proteins containing all the various classes of DNA-binding loop2 sequences that were available were generated. To ease this process a ‘cassette’ structure to the Rb69 clones were engineered, having a unique Bal I restriction enzyme site on one side and a KpnI restriction site on the other. Synthetic oligonucleotides were cloned into Rb69 UvsX clones cut with these enzymes. The clones were generated as illustrated schematically in FIG. 21. Problems were encountered when attempting to express some of these proteins. Purified protein for the RecA-substituted loop could not be recovered, and the KVP40-substituted loop aggregated during dialysis and could not be re-solubilised effectively afterwards. Of the remaining proteins, the Aeh1, Rb16/Aeh1 and Cyanophage-substituted loops were expressed well but had no activity in the assays. The phage 133-substituted loop did possess, albeit weak, activity in the assays.

Without intending to be bound by any theory, these clones were possibly slightly at a disadvantage relative to the studies done on T4 and T6 DNA-binding loops because in this case they were engineered into a wild-type Rb69 backbone rather than one containing H64S, and a more acidic C-terminus. No engineering of other parts of the Walker A motif were made either. Nevertheless the results provide a useful diagnostic on the likely tolerance of altered sequences in this region. First, it was noted that like T4 and T6, phage 133 DNA-binding loop could confer some activity to the hybrid protein. It can be concluded that to some extent there is a general tolerance to the short ‘standard’ loop lengths found in most sequenced phage UvsX molecules. Second, it was noted that Aeh1 failed, but this protein has a very unexpected mutation of the asparagine that begins the loop and is otherwise very highly conserved. It is anticipated that other substitutions would be necessary in order to tolerate this change. Finally, neither the cyanophage, nor the RecA loop appeared to be tolerated. In the case of the RecA loop this is not unexpected as this loop does not even conserve the loop length, being longer in RecA. Without intending to be bound by any theory, there may be problems for this protein to fold correctly, or it may tend to aggregate. The cyanophage loop is the same length as the parent Rb69 loop, however the sequence is almost completely different. As the cyanophage proteins are very diverged from Rb69, and have radically different Walker A motifs, it is expected that changing this loop in isolation will not suffice to generate a functional molecule.

T6 UvsX and Derivatives Exhibit UvsY-Independent Activity

An experiment was performed investigating the effects of modified DNA backbones in oligonucleotides used in RPA, in particular to assess whether they influenced a need for UvsY. In the course of this work it was observed that UvsY was not essential for the amplification of DNA in experiments performed with T6 UvsX with the histidine 66 to serine mutation (T6 H66S). This unexpected phenomenon was further investigated, and the data described below confirmed that this property is substantially, although perhaps not entirely, attributable to the T6 origin of the recombinase species in the reaction.

FIG. 52 illustrates an experiment performed to assess whether UvsY was required for amplification of DNA fragments from a template (generated by PCR) using a variety of primers. The experiment clearly indicated that for 3 of the 4 primer pairs used in this experiment (all combinations shared one common primer paired with an opposing primer a variable distance away in the template) products were generated in the absence of UvsY which were of the expected molecular weight. A follow-up experiment is shown in FIG. 53 in which the same template was employed, but some variable primer combinations were used (see legend). In this case 4 of the 5 combinations were successful regardless of the presence or absence of UvsY. Differences in product intensity were observed, and in some cases products were more abundant in the absence of UvsY. The results indicate UvsY is partially dispensable in at least some amplification reactions performed with this recombinase (T6 H66S), SSB (Rb69 gp32), PEG 35,000 and polymerase (Sau Pol).

Investigations were extended to templates which were provided as complex genomic DNA. Of particular concern was that the extraordinary efficiency observed with the MS2 template might arise because this template had first been generated by PCR and might contain denatured or single-stranded templates. These situation could remove some ‘constraints’ placed on initiating RPA on true embedded sequences which are potentially difficult because of their tendency to from topologically strained structures during early cycles of amplification. The experiment shown in FIG. 54 depicts the amplification of DNA from human genomic DNA using pairs of primers (one common primer) which generate progressively larger fragments. In this case the results were rather more variable than observed with the MS2 template. However, at least two of the combinations generated fragments that were considered to be the expected length even when UvsY was omitted (all reactions functioned in the presence of UvsY). This work was extended in the experiment shown in FIG. 55. Once again, in some cases, DNA products of the expected sizes were generated in paired reactions even when UvsY was omitted, and once again there was significant variability on the outcome depending on the primer pairs and/or anticipated product size. It was believed that reactions 2 and 4 were successful in both cases.

Another set of experiments were performed to assess whether this remarkable and previously unnoticed activity, believed to be attributable to of T6 derivative recombinase, (and possibly associated factors used here) extended to a difference in requirement for polyethylene glycol. FIG. 56 shows that despite a partial resistance to the need for UvsY, the omission of PEG results in the absence of significant DNA synthesis. It was concluded that PEG was still required to achieve useful DNA amplification from low target concentration samples.

Next assessed was whether the type of gp32 employed affected the UvsY-independent nature of these amplification reactions. FIG. 57 shows the results of an experiment in which T4 gp32 is employed instead of Rb69 gp32. As shown in FIG. 57, DNA was still amplified in the presence of T4 gp32, albeit with slightly different ratios of products. FIG. 58 extends this work and shows that DNA is still synthesized in a heterologous system employing Aeh1 gp32, although no products of the expected size were generated in the absence of UvsY. Note however that DNA of some description was made in the absence of UvsY which was consistent with a significant biochemical difference between these reactions and earlier reactions using all T4 reagents. In the models described herein, to synthesise/amplify any DNA visible on gels at endpoint a minimum number of loaded recombinase filaments are required, which were considered to be too few in the absence of UvsY acting as a re-loading/stabilizing agent. Thus, it was concluded that exchanging gp32 species does influence the efficacy of reactions under these conditions, but that in all cases DNA synthesis does occur even in the absence of UvsY in contrast to earlier results attained with T4 reagents. It was concluded that the T6-derivative UvsX is primarily responsible for permitting high-loading of recombinase filaments in contrast to the situation with T4 UvsX. This presumably could reflect difference in the DNA-binding domains as well as inter-subunit surfaces involved in stabilizing the co-operative filament structure.

This difference in UvsX behaviour was further confirmed in the experiment shown in FIG. 59, showing a complete absence of DNA synthesis when T4 UvsX is substituted for T6 H66S UvsX, and then UvsY is omitted. Similar results were obtained in the experiment shown in FIG. 60 in which a similar experiment is performed but using T4 gp32 throughout—T4 UvsX absolutely requires UvsY while T6 H66S does not in these experiments. A kinetic experiment is shown in FIG. 61. As shown in FIG. 61, detection kinetics are moderately similar between T4 and T6 H66S experiments. However when UvsY is omitted there is little consequence for the T6 H66S amplification kinetics, while the T4 recombinase shows no activity. In other experiments with other templates, an obligate need for UvsY even when using T6 H66S, was noted. Thus it was concluded that UvsY is only partially dispensable when using this recombinase, and it can still improve reaction behaviour and play a role in robust and consistent RPA behaviour between targets.

Next, investigations into whether this unusual property was observed with unmodified T6 UvsX, and whether it extended to other recombinases (such as Rb69 UvsX and Aeh1 UvsX) were performed. FIG. 62 shows very clearly that DNA is efficiently synthesized with at least one oligonucleotide combination when T6 recombinase is employed in the absence of UvsY. It was concluded that the unusual property of UvsY-independence not observed with T4 UvsX extends to the unmodified T6 UvsX, albeit there were differences in product accumulation levels between T6 UvsX and T6 H66S UvsX confirming their biochemical distinction.

FIG. 63 shows that results of an experiment to determine whether Rb69 UvsX could operate in the absence of UvsY. While caution is advised on interpretation of the results because one of the amplicons did not amplify even with UvsY, the principle observation was the lack of DNA generated when UvsY was omitted. Without intending to be bound by any theory, this implies that, like T4 UvsX, Rb69 UvsX cannot readily support efficient amplification without the presence of UvsY. FIG. 64 extends this analysis to the employment of phage Aeh1 components. As shown in FIG. 64, amplification is efficient in a heterologous system comprising Aeh1 UvsX, Aeh1 UvsY and Rb69 gp32, however if Aeh1 UvsY is omitted no amplification is seen. Next, the activity of a modified Rb69 UvsX containing, amongst other things, the DNA binding loop2 sequence of T6, was assessed. This experiment was performed to assess whether the activity of T6 derivatives might arise from the distinct T6 DNA binding loop2 sequence. In this case, no amplification in the absence of UvsY was observed, although caution is advised as amplification seemed rather weak in the presence of UvsY. However, taken at face value, this result does not support that the T6 DNA binding loop 2 is wholly responsible for the unusual behavior of T6 UvsX and its derivatives, or that this property cannot be trivially transferred in isolation.

These results collectively show that T6 UvsX and its derivatives are unusual insofar as when co-incubated in the presence of gp32 species of various types (T4, Rb69 and Aeh1) it is capable of supporting significant recombination activity without a need for UvsY. Without intending to be bound by any theory, existing models suggest that a limiting component of recombinase-driven amplification systems is the concentration of recombinase-loaded filaments. These are not considered to be abundant when T4 UvsX is co-incubated in the presence of T4 gp32, and in the absence of UvsY and crowding agents. However the evidence suggests that for T6 UvsX this competitive environment is perhaps shifted in the favor of recombinase, so much so that UvsY can be dispensed with in some cases. For this to occur, it could be inferred that T6 UvsX may have a higher affinity for single-stranded DNA than T4 UvsX, and/or that it is less likely to disassemble from filaments as a consequence of active ATP hydrolysis. In turn these properties could arise due to higher affinity of the DNA binding elements of the recombinase for nucleic acids, and/or via higher affinity between protein subunits in the filaments leading to a reduction in disassembly behaviour. However, it is noteworthy that reactions appeared more robust on the whole when UvsY was included. Occasionally, in its absence, DNA was synthesized but products of the expected size did not accumulate. This outcome could reflect an abundance of active filaments but some other fundamental flaw in the RPA reaction cycle.

Without intending to be bound by any theory, two possible mechanisms to explain why UvsY enhances RPA functionality even when it is not strictly required for some amplification activity are proposed herein. First, UvsY could confer full and even loading of filaments on oligonucleotides ensuring that they are coated to their 5′ ends, and undergo efficient recombination along their length. In the absence of UvsY, according to this rationale, filaments may only be partially loaded and this could lead to a situation in which recombination leads to constrained intermediates (no free unwinding possible at the substrate 5′ ends) most of the time which are unstable and lead to disassembly of recombinase/synthesis intermediates before complete synthesis along a target has occurred. This could favor very short products such as primer dimers that require little processive DNA synthesis. A second alternative is that UvsY plays an active role in the DNA synthesis process as it is ongoing. For example, UvsY could promote recombinase-loading of the outgoing strand and re-invasion to cause a ‘bubble migration’ activity. Such bubble migration synthesis could act to decrease topological strain on the synthetic complex. Similarly, the processivity of elongation complex might rely on accessing the 3′ end of DNA which is still partly coated with UvsX, and this might require UvsY presence. In any case, the data support the notion that UvsY may play a role in the RPA process that is more sophisticated than simply increasing the steady state number of recombinationally active filaments in the reaction environment.

Furthermore the use of different gp32 species may influence the UvsY-dependence of RPA reactions. Experimental data provided here, including competition oligonucleotide competition data and thermal stability data presented below, suggest that T4 gp32 may have a particularly high affinity for DNA when compared to Rb69 gp32 and Aeh1 gp32. Thus, according to a model in which UvsX and gp32 compete for common substrates as described earlier, it may be beneficial for the recombinase if a gp32 with a lower DNA affinity is employed. Thus Rb69 gp32 is likely to favor recombinase-loading in such a competitive environment.

Manganese can Support RPA Reactions

Manganese can replace magnesium ions to support DNA amplification by the RPA system. In particular the useful range of manganese ions for supporting robust amplification is significantly lower than that found for magnesium. The most effective amplification occurs when manganese is present at roughly 1 to 3 mM (FIG. 47). Higher concentrations are progressively inhibitory to significant product accumulation. These low levels of supporting ion are something of a surprise as in some cases this is an insufficient quantity to saturate the abundant ATP and dNTP species in the reaction (ATP is used at 3 mM).

Heparin can Act as a Noise-Suppressing Reagent

The effects of heparin on RPA reactions were investigated. This was in part in an effort to establish the resistance of RPA reactions to agents commonly found in clinical and environmental samples. It was surprising to discover that RPA was rather resistant to the inclusion of heparin in the amplification reactions. Indeed it even appeared that heparin could improve the outcome of RPA reactions, apparently by reducing the rate at which primer artefacts accumulate in RPA reactions. FIG. 49 reveals how the inclusion of heparin at 20 ng/μl results in a delay in the accumulation of primer artefacts which appear if RPA is permitted to run without a target present in the reaction. Using a probe-based sensing approach, inclusion of heparin in RPA was tested to determine whether it would improve the behaviour of RPA reactions. FIG. 50 explores the effects of including heparin in amplification reactions. The following phenomena are observed: the time of onset of signal detection are similar regardless of the presence of heparin, however when present heparin leads to more consistent time of onset of detection at low copy numbers. Heparin slightly decreases the total signal which develops in the reaction. It was concluded that probably heparin acts as a ‘sink’ for UvsX or other DNA binding proteins and can help to buffer it from excessive activity which may benefit noise rather than signal under certain circumstances.

E. coli Exonuclease III can Function as a Primer Polishing Agent in RPA

E. coli endonuclease IV (Nfo) or E. coli exonuclease III were included in RPA reactions that include proprietary fluorescent probe sensing system (Piepenburg et al., 2006) as an agent to process abasic-site containing probes. However during investigations into novel probe structures some surprising and unexpected observations were made, namely that supposedly 3′-blocked primers could be efficient amplification primers when used in reactions containing exonuclease III, and perhaps to a lesser extent if containing endonuclease IV (Nfo) (see FIG. 51). It was hypothesized that blocked primers employed in these cases were being unblocked by the activity of the enzymes. Both of these enzymes have reported activities which include 3′-exonuclease activity as well as having 3′-diesterase or phosphatase activities. Without intending to be bound by any theory, it is likely they either ‘polish’ the blocking group from the final base, or remove the final base with the blocking group on it. It is not possible to distinguish between these possibilities from these experiments. However the potential ability to ‘unblock’ primers in a sequence-dependent manner has certain potentially useful applications.

S. aureus Pol I Large Fragment is Functional in RPA Reactions

RPA works efficiently with Bsu polymerase as previously shown (See Piepenburg et al. U.S. Ser. No. 10/931,916). It has also been shown to function with the Klenow fragment of E. coli Pol I, and with Bst polymerase. Other polymerases were examined in attempts to extend the breadth of polymerases that may be used in RPA reactions. The polymerases examined included repair class polymerases, and polymerases which lack proof-reading activity. The large fragment of such polymerases, as opposed to the full protein, were also examined. A sequence corresponding to the S. aureus Pol I was identified in the Genbank entry locus BX571857 which is the genome sequence of methicillin-sensitive S. aureus strain MSSA476. The complete polymerase coding sequence corresponds to the complement to positions 1740769 to 1743399 of the genomic sequence and the putative encoded polypeptide has the TrEMBL accession number Q6G8N6. A fragment of this coding region was amplified from MSSA476 genomic DNA corresponding to position 865 to 2631 of the coding region, thus omitting the first 288 amino acid residues which correspond principally to the 5′-3′ exonuclease domain. This fragment was cloned into pET21+ and included a hexahistidine-encoding tag incorporated into the PCR primers at the 5′ end. This protein expressed efficiently and was readily purified on Ni-NTA agarose. This protein was tested in RPA reactions as shown in FIG. 48. It was observed that the S. aureus enzyme (referred to as Sau polymerase) works very well and seems at least as efficient as the Bsu polymerase.

gp32 Activity

As demonstrated below, novel activity assays for gp32 proteins demonstrate their distinct biochemical activities. gp32 proteins were derived from several different bacteriophages. In one experiment, gp32 activity was assessed by establishing a reaction environment in which the mass of gp32 contained in the reaction was titrated until it was just limiting in activity as assessed by a nuclease-protection assay. FIG. 66 illustrates such assay, which was performed to determine the quantity (mass) of Rb69 gp32 required to inhibit the cutting of a reporter probe oligonucleotide by the endonuclease IV (Nfo) of E. coli. In this assay, cutting was monitored by rising fluorescence which occurs as a consequence of nucleolytic attack on a tetrahydrofuran (abasic mimic) positioned between a fluorophore and dark quencher in the probe. In the absence of gp32 the probe was cut so rapidly that by the time the tube was transferred to the fluorometer for measurement it was already almost completely degraded (high fluorescence). Conversely, when 250 ng/μL of Rb69 gp32 was included in the reaction, cutting was completely abolished and a flat line resulted throughout the assay time (100 seconds). Intermediary quantities of the gp32 protein resulted in fluorescence increase curves of various slopes consistent with a strict relationship between protein mass and protective capacity. The results demonstrate the utility of this assay in establishing the ‘activity’ of a gp32 preparation.

As shown in FIG. 66, it is possible to establish a ratio of probe oligonucleotide and gp32 protein that is on the boundary of complete protection, such as between 83 and 100 ng/μL. At this concentration of gp32 cutting occurred, but only slowly, and any changes in gp32 activity were likely to be easily observed by difference in cutting rate. At such a concentration, the reaction was challenged with additional added reagents or changes in environmental conditions, such as temperature, and the efficacy of gp32 in probe protection was assessed. FIG. 67 shows the results of an experiment in which the consequences of challenging the reaction with additional single-stranded or double-stranded DNA were assessed. In this experiment, the effects of these challenges on Rb69 gp32, T4 gp32 and Aeh1 gp32 were compared. In all cases challenge with competitor ssDNA at a defined time resulted in a sharp increase in probe attack.

The results demonstrate that the distribution of gp32 must be highly dynamic, supporting the notion that both association and dissociation events occur frequently in RPA reactions (although in the presence of crowding agents and other RPA reagents the kinetics may be altered). While this competitive effect of ssDNA was strong and similar between different gp32 species, significant differences were noted when the system was challenged with double-stranded DNA. When challenged with 10 times the mass of dsDNA (compared to probe) Aeh1 and RB69 gp32 showed only very slight increases in cutting activity. In contrast T4 gp32 showed a very significant increase in cutting activity. While not intending to be bound by any theory, the results suggest that the relative affinities of the gp32 species to double-stranded DNA were significantly variant. These results further suggest that there are could be significant differences in the late RPA reaction behaviour depending on the species of gp32. Rb69 or Aeh1 gp32 are likely to be more strongly partitioned between single-stranded and double-stranded DNA, while T4 gp32 in likely to be titrated out onto the duplex products. This may account for some of the improved activity noted with Rb69 gp32 in some RPA reactions. It is possible that T4 gp32 simply has a higher overall DNA affinity, which would be consistent with the results of the next experiment detailed below.

In another variation of the probe protection assay the effects of temperature on the activity of the gp32 in protecting the probe were investigated. FIG. 68 shows the effects of progressively increasing the temperature of the reaction environment over time and reveals that at a certain point the protective properties of the gp32 suddenly decrease. This presumably represents the upper temperature at which the protein functions efficiently. It was noted that the profiles are markedly different between the 3 species tested here. Aeh1 gp32 became less effective above about 40 degrees centigrade and losing protective capacity very quickly above this temperature. By 42 degrees it lost almost all of its activity. In contrast Rb69 gp32 retains full activity up until about 42 degrees and then slowly starts to lose activity. While compromised, it still affords some protective capacity up until 47 degrees in this assay. The most powerful protective capacity was, however, observed for T4 gp32 which only started to show a slight decrease in effectiveness at 49 degrees, the highest temperature assayed in this experiment. Thus was deduced that the operational temperature range for these 3 proteins is clearly and measurably distinct. This should have some considerable significance when deciding which gp32 species is most suitable for a given application, and may reflect both the thermal stability of the protein itself as well as the relative DNA binding affinity of the protein.

It is understood that “acid C-term,” acidic C terminus, acid N-term, and acidic N terminus refer to the optional addition of one or more acid amino acids, such as (LDE)_(n) or (LSD)_(n) where n=1 to 4 or 10 or fewer acidic amino acids to the C or N terminus of the protein. In addition, any of the proteins described anywhere in this specification, including the recombinase (e.g., UvsX), recombinase loading agent (e.g., UvsY), and single stranded binding protein (e.g., gp32) may optionally include a His tag at the N terminus, at the C terminus, or between the N terminus and C terminus of the protein in addition to any other modification (such as acidic C or N terminus). His tag is understood to mean 10 or fewer amino acids comprising Histidines in series or Histidine and Glutamine (HQ, or QH) in series—in a preferred embodiment, the number is 6. Furthermore, His tags may also refer to amino acids such as HQHQHQHQHQ (SEQ ID NO:83) which is less than 10 amino acids in length such as HQHQHQ (SEQ ID NO:84). For example, if a protein has both an acidic C terminus and a C-terminus histidine tag, the protein may have a configuration such as [protein]-[acidic residues]-[histidine tag] or such as [protein]-[histidine tag]-[acidic residues]. Alternatively, a protein with both an acidic N terminus and a N terminus histidine tag may have a configuration of [acidic residues]-[histidine tag]-[protein] or such as [histidine tag]-[acidic residues]-[protein].

EXAMPLES

The invention, having been generally described, may be more readily understood by reference to the following examples, which are included merely for purposes of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention in any way. Other aspects, advantages, and modifications are within the scope of the following claims.

Example 1 Cloning and Protein Expression

All DNA manipulations were performed using standard techniques, in particular cloning using PCR, PCR-based mutagenesis procedures, and standard restriction digestion and ligation. Sequencing was performed by Lark technologies Ltd, Saffron Walden, UK. All proteins were expressed in E. coli and purified in 1M NaCl following lysis using lysozyme at 1 mg/ml and 2-3 freeze thaw cycles. Ni-NTA resin was purchased from Qiagen.

Amplification Reactions

The conditions for individual amplification reactions are described in the detailed descriptions provided below. In general reactions were monitored in real-time either by the inclusion of SYBR green dye, or more often by employment of a probe-based approach developed by us (see Piepenburg et al. 2006). In this case the probe is a third DNA primer which contains an internal tetrahydrofuran residue (abasic site mimic) flanked by a fluorophore and a quencher. On hybridization to amplified DNA this probe becomes a substrate for the endonucleolytic activity of endonuclease IV (Nfo) or exonuclease III which are enzymes included in the reaction.

The sequence of fluorescent probes described here are as follows:

SATamra1 (SEQ ID NO: 85) 5′-tgttaattgaacaagtgtacagagcatt(T)a(H)ga(q1)tatgcgtggag-Biotin-3′ SATamra2 (SEQ ID NO: 86) 5′-tgttaattgagcaagtgtatagagcatt(T)a(H)ga(q2)tatgcgtggag-Biotin-3′ BsFlc (SEQ ID NO: 87) 5′-catgattggatgaataagctgcagc(F)g(H)t(q3)aaaggaaactta-Biotin-3′

Where (T) is dT-TAMRA, (F) is dT-Fluorescein, (H) is THF, (q1) is dT-BHQ1, (q2) is dT-BHQ2, (q3) is dT-DDQ1. Nfo enzyme was used at 200 ng/μl, but almost all probe-based experiments employed exonuclease III at 65 ng/μl. Excitation/detection was at 485/525 nm (SYBR green or probe BsFlc) or 530/575 nm (SATamra1/2). Measurements were taken every 30 or 45 seconds. Fluorescence probe data was normalised against water controls, and the pre-amplification baseline was adjusted. In general the logarithm of the normalised fluorescence read-out was plotted against time for the probe-based experiments.

Amplification primers: Bacillus subtilis:

(SEQ ID NO: 88) J1 5′-acggcattaacaaacgaactgattcatctgcttgg (SEQ ID NO: 89) K2 5′-ccttaatttctccgagaacttcatattcaagcgtc

MRSA:

sccIII (SEQ ID NO: 90) 5′-ccaatatttcatatatgtaattcctccacatctca orfx45a (aka orfx) (SEQ ID NO: 91) 5′- cccaagggcaaagcgactttgtattcgtcattggcggatcaaacg sccII-35 IV (SEQ ID NO: 92) 5′- ctcaaagctagaactttgcttcactataagtattc

(SEQ ID NO: 93) MS2 down RT2-5′ - cttaagtaagcaattgctgtaaagtcgtcac (SEQ ID NO: 94) MS2 down 5-5′ - ccagtagcgacagaagcaattgattggtaaatt (SEQ ID NO: 95) MS2 up 2-5′ - ttccgactgcgagcttattgttaaggcaatg (SEQ ID NO: 96) MS2 up 4-5′ - cctcgcgatctttctctcgaaatttaccaatca (SEQ ID NO: 97) MS2 up 5-5′ - ccatgtcgaagacaacaaagaagttcaactctt (SEQ ID NO: 98) MS2 up 6-5′ - catctactaatagacgccggccattcaaacatg (SEQ ID NO: 99) MS2 up 7-5′ - cccgattccctcagcaatcgcagcaaactccgg

Apolipoprotein B:

ApoB4 (SEQ ID NO: 100) 5′- cagtgtatctggaaagcctacaggacaccaaaa ApoB300 (SEQ ID NO: 101) 5′- tgctttcatacgtttagcccaatcttggatag ApoB3 (SEQ ID NO: 102) 5′- tgacaagtgtgctataaacctggcctaccagag ApoB7 (SEQ ID NO: 103) 5′- ttgatacattcggtctcgtgtatcttctata ApoB10 (SEQ ID NO: 104) 5′- gatacattcggtctcgtgtatcttctagg

Clones were constructed by PCR using genomic DNA of T6 phage, Rb69 phage, Aeh1 phage, or phage KVP40. FIG. 1 shows the schematic layout of novel clones encoding diverse recombination machinery from the myoviridae. A modified pET21+ plasmid (Novagen) was used, and hexahistidine tags were engineered into the PCR primers to encode in-frame tags at either the N terminus (UvsY proteins) or at the C terminus (UvsX and gp32 proteins). In alignments and discussions later the amino acid residue numbers refer to the position in the native proteins as documented in the relevant databases. In the case of UvsY there will be 6 histidines and a methionine preceding this in the clones used.

Example 2 Primary Sequence Alignment of Diverse Recombinase Proteins

Primary Sequence Alignment of T4 UvsX and E. coli RecA

The web-based tool MAFFT (accessed via the Expasy proteomics server) was used to align the primary polypeptide sequences of T4 UvsX and E. coli RecA, as shown in FIG. 2. This alignment was consistent with those generated and discussed elsewhere. Based on the known crystal structure of E. coli RecA the position of three regions of interest namely the Walker A motif involved in ATP binding and hydrolysis, the mobile DNA binding loop 1, and the mobile DNA binding loop 2 sequences are boxed. Under the alignment symbols indicate amino acid identity between all homologs (*), conserved substitutions (:), or semi-conserved substitutions (.).

Model of RecA Structure with Superimposition and Labelling of Equivalent T4 UvsX Residues

A model of the RecA nucleoprotein filament was generated using CN3D and a dataset downloaded from the NCBI database, PDB entry 1N03 (associated citation Vanloock M S et al., Structure 2003 February; 1 (2):187-96). Using the alignment in FIG. 2 the putative position of T4 UvsX residues was mapped to this RecA structure as an exercise in providing insight into the possible position of UvsX amino acids of interest and their proximity to one another. FIG. 3 shows the model of RecA structure with superimposition and labelling of equivalent T4 UvsX residues based on primary sequence alignment. FIG. 3A shows the screenshot looking down the axis of the model RecA filament with the central hole being the approximate location of bound DNA. The approximate location of the Walker A motif and mobile DNA binding loops is indicated for a single subunit and is on the surface facing the nucleic acid. FIGS. 3B and 3C show two zoomed shots are taken of the region to which ATP is bound on the surface indicated in (A). the putative positions of T4 UvsX residues G60, S64, S67, F69, G70, H195, and M208 are indicated in FIG. 3. Also indicated are the approximate locations of the beginning and end of mobile DNA-binding loop 2. That these amino acids are positioned exactly as shown in this model is unlikely given the significant divergence between RecA and UvsX, however these approximations are probably of meaningful utility for the study herein.

Primary sequence alignment of T4 and T6 g32 and UvsY proteins

The web-based tool MAFFT (accessed via the Expasy proteomics server) was used to align the primary polypeptide sequences of T4 and T6 gp32 and UvsY proteins, as shown in FIG. 4. This alignment revealed only small differences between these proteins. The UvsY proteins had only 2 highly conservative substitutions. Under the alignment symbols indicate amino acid identity between all homologs (*), conserved substitutions (:), or semi-conserved substitutions (.).

Primary Sequence Alignment of Diverse UvsX Proteins

The web-based tool MAFFT (accessed via the Expasy proteomics server) was used to align the primary polypeptide sequences of T4, T6, phage 133, Rb69, Aeh1, Ae65, KVP40, Rb43, PSSM2, and PSSM4 UvsX proteins, as shown in FIG. 5. Several regions of interest were boxed, namely the Walker A motif (or ‘P-loop’) involved in DNA binding and hydrolysis, the mobile DNA binding loop 1, and the mobile DNA binding loop 2. Certain residues under discussion have been highlighted. All amino acid differences between T4 and T6 UvsX are shown in bold. Under the alignment symbols indicate amino acid identity between all homologs (*), conserved substitutions (:), or semi-conserved substitutions (.).

Primary Sequence Alignment of Diverse UvsY Proteins

The web-based tool MAFFT (accessed via the Expasy proteomics server) was used to align the primary polypeptide sequences of T4, T6, phage 133, Rb69, Aeh1, KVP40, Rb43, PSSM2, and PSSM4 UvsX proteins, as shown in FIG. 6. In this alignment the PSSM4 sequence was derived from our own translation of the genomic DNA, the NCBI entry apparently erroneously omitting the first 43 residues from the polypeptide sequence. Under the alignment symbols indicate amino acid identity between all homologs (*), conserved substitutions (:), or semi-conserved substitutions (.).

Primary Sequence Alignment of Diverse gp32 Proteins

The web-based tool MAFFT (accessed via the Expasy proteomics server) was used to align the primary polypeptide sequences of T4, T6, Rb69, Aeh1, KVP40, Rb43, PSSM2, and PSSM4 gp32 proteins, as shown in FIG. 7. In this alignment the PSSM2 sequence was derived from our own translation of the genomic DNA, the NCBI entry apparently erroneously omitting the first 25 residues from the polypeptide sequence. Under the alignment symbols indicate amino acid identity between all homologs (*), conserved substitutions (:), or semi-conserved substitutions (.). Also indicated by arrows are the positions of residues implicated in the co-ordination of zinc in T4 gp32. Also indicated by a line above the sequence is a common sequence, FKRK (or FKRQ in Rb43) which is absent in cyanophage gp32 proteins, and is implicated in co-operative binding as is the zinc atom of T4 gp32. Lack of co-ordinating residues in cyanophage gp32 proteins suggests that these proteins may not require metals such as zinc, cobalt, nickel etc. for activity. The re-organised status of the KVP40 metal-binding region suggests that this protein may not bind zinc, but rather a different metal atom, or that is may show altered requirements for zinc during growth, or altered sensitivity to replacement assault by competitor metal atoms.

Example 3 T6 UvsX Substituted for T4 UvsX in RPA Reactions Using Heterologous Components

RPA reactions were configured using primers Rs8179145-2 and Rs8179145-3 whose sequences are indicated. Target DNA was human genomic DNA, and reaction conditions were as follows: 100 mM potassium acetate, 50 mM Tris Acetate pH 8.3, 50 mM phosphocreatine, 3 mMP ATP, 200 μM dNTPs, 300 nM Rs8179145-2 primer, 300 nM Rs8179145-3 primer, 150 ng/μL T4 or T6 UvsX, 1000 ng/ng/μL T4 gp32, 40 ng/μL T4 UvsY, 42 copies of human genomic DNA, 5% Carbowax 20 M, and 32 ng/μL Bsu polymerase. After 90 minutes samples were purified via centrifugation through a Qiagen PCR product clean-up column. Purified samples were analyzed on an ethidium bromide stained agarose gel. The expected amplicon size from the human locus Rs817945 was 205 bp. Asterisks on the gel shown in FIG. 8 indicate the position of the expected band, 205 bp and the position of marker bands is indicated on the left. As shown in FIG. 8, T6 UvsX can effectively be substituted for T4 UvsX in RPA reactions using heterologous components.

RPA reactions were established to compare the kinetics of T6 and T4 UvsX using SYBR green dye, using primers J1 and K2 under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 120 ng/μl UvsX of T4 or T6, 30 ng/μl UvsY, 900 ng/μl gp32, 30 ng/μl Bsu polymerase, 5% Carbowax 20M, 300 nM amplification primers, 1:50,000 dilution from stock of SYBR green (Invitrogen). Reactions were established on ice in a 96-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a top-reading probe. Samples contained either no target (water) or 50 or 5000 copies of B. subtilis genomic DNA containing the target sequence. Samples contained either T4 or T6 UvsX, and the recombinase and presence of target is shown in the legend. Each sample was run in duplicate.

Positive signals developed in all samples during the 60 minute incubation, and the time of signal increase was earlier in the target-containing samples than in non-target samples as expected. As shown in FIG. 9, the time at which signal increase was first detected was similar between T4 and T6 samples. However the curves developed with different slopes and final maxima. T6 gave less sharp signal accumulation and less high final signals.

RPA reactions were also established to compare the kinetics of T6 and T4 UvsX using fluorescent probe, using primers orfx45a (120 nM) and sccii35IV (480 nM) under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 120 ng/μl UvsX of T4 or T6, 30 ng/μl UvsY, 900 ng/μl gp32, 50 ng/μl Bsu polymerase, 5% Carbowax 20M, 120 nM fluorescent probe SATamra2. Exonuclease III was included at 65 ng/μl. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either no target (water) 100, or 1000 copies of MRSA 3 (mecI) genomic DNA containing the target sequence. Samples contained either T4 or T6 UvsX, and the recombinase and presence of target is shown in the legend. Each sample was run in duplicate.

Positive signals developed in the template positive samples during the 90 minute incubation, and the time of signal increase was earliest in the highest target-containing samples. As shown in FIG. 10, the time at which signal increase was first detected was similar between T4 and T6 samples, particularly for the 1000 copies samples, however the curves developed with different slopes and final maxima. T6 gave less sharp signal accumulation and less high final signals.

Example 4 Engineered T6 UvsX Protein Constructs

The parent plasmid clone containing T6 UvsX in a modified pET21+ vector was altered using standard PCR mutagenesis protocols. A schematic layout of the relation of the coding region/primary polypeptide sequence to putative structural elements is shown at the top of FIG. 11. Modifications were made to three regions which are shown as boxes on the schematic, the Walker A motif, the DNA binding loop1 and, DNA binding loop2. Several regions and amino acids were targeted and these are indicated on the lower schematics next to the name given to the clone. Numbers refer to the position of the amino acid in the wild type T6 UvsX protein, hence H66S means that the histidine present as amino acid 66 in wild type T6 was altered to a serine. On the left of the FIG. 11, a simple representation of the general activity of the protein produced for this clone when tested in RPA assays is shown.

Comparison of T6 UvsX H66S and Wild Type T6 UvsX

RPA reactions were established to compare T6 UvsX H66S and wild type T6 UvsX using primers J1 (120 nM) and K2 (480 nM) under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 120 ng/μl UvsX of T4 or T6 UvsX H66S, 45 ng/μl T4 UvsY, 900 ng/μl T4 gp32, 30 ng/μl Bsu polymerase, 5% Carbowax 20M, 120 nM fluorescent probe BsFlc. Exonuclease III was included at 65 ng/μl. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either 100, or 1000 copies of B. subtilis genomic DNA containing the target sequence. Samples contained either T4 or T6 UvsX H66S, and the recombinase and presence of target is shown in the legend in FIG. 12. Each sample was run in duplicate.

The sequence of T6 UvsX H66S is as follows: MSIADLKSRL IKASTSKMTA ELTTSKFFNE KDVIRTKIPM LNIAISGAID GGMQSGLTIF AGPSKSFKSN MSLTMVAAYL NKYPDAVCLF YDSEFGITPA YLRSMGVDPE RVIHTPIQSV EQLKIDMVNQ LEAIERGEKV IVFIDSIGNM ASKKETEDAL NEKSVADMTR AKSLKSLFRI VTPYFSIKNI PCVAVNHTIE TIEMFSKTVM TGGTGVMYSA DTVFIIGKRQ IKDGSDLQGY QFVLNVEKSR TVKEKSKFFI DVKFDGGIDP YSGLLDMALE LGFVVKPKNG WYAREFLDEE TGEMIREEKS WRAKDTNCTT FWGPLFKHQP FRDAIKRAYQ LGAIDSNEIV EAEVDELINS KVEKFKSPES KSKSAADLET DLEQLSDMEE FNE (SEQ ID NO:105).

As shown in FIG. 12, positive signals developed in the samples during the 90 minute incubation, and the time of signal increase was earliest in the highest target-containing samples. Signals developed earlier in the T6 UvsX H66S—containing samples, particularly for the 1000 copies samples, and the curves developed higher final maxima. Based on this study, it was concluded that T6 UvsX H66S performs better in these assays than wild type T6

UvsX. However the slope of the signal accumulation using this system was similar between the 2 proteins, and therefore it is unlikely that T6 UvsX H66S exactly reproduces the activity of T4 UvsX in this assay.

Kinetic Behaviour of Other Mutants of T6 UvsX

RPA reactions were established using mutant T6 UvsX components, using primers J1 (120 nM) and K2 (480 nM) under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 120 ng/μl UvsX of T6 or T6 UvsX H66T or T6 UvsX M71F/S72G or T6 UvsX S164V/A166S, 45 ng/μl T4 UvsY, 1000 ng/μl T4 gp32, 30 ng/μl Bsu polymerase, 6% Carbowax 20M, 120 nM fluorescent probe BsFlc. Exonuclease III was included at 65 ng/μl. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either water or 200 copies of B. subtilis genomic DNA containing the target sequence as indicated in the legend.

As shown in FIG. 13, positive signals developed in some samples during the 90 minute incubation. Signals developed earliest in the T6 UvsX S164V/A166S and then wild-type samples. Signal accumulated much later in the T6 UvsX H66T sample, and no signal accumulated in the T6 UvsX M71F/S72G sample. It was concluded that T6 UvsX S164V/A166S performs well in these assays, however in some later experiments little or no difference to the wild type T6 UvsX was found. It was further concluded that T6 UvsX H66T has poor activity, and T6 UvsX M71F/S72G is inactive.

The sequence of T6 UvsX S164V/A166S is as follows: MSIADLKSRL IKASTSKMTA ELTTSKFFNE KDVIRTKIPM LNIAISGAID GGMQSGLTIF AGPSKHFKSN MSLTMVAAYL NKYPDAVCLF YDSEFGITPA YLRSMGVDPE RVIHTPIQSV EQLKIDMVNQ LEAIERGEKV IVFIDSIGNM ASKKETEDAL NEKVVSDMTR AKSLKSLFRI VTPYFSIKNI PCVAVNHTIE TIEMFSKTVM TGGTGVMYSA DTVFIIGKRQ IKDGSDLQGY QFVLNVEKSR TVKEKSKFFI DVKFDGGIDP YSGLLDMALE LGFVVKPKNG WYAREFLDEE TGEMIREEKS WRAKDTNCTT FWGPLFKHQP FRDAIKRAYQ LGAIDSNEIV EAEVDELINS KVEKFKSPES KSKSAADLET DLEQLSDMEE FNE (SEQ ID NO:106).

Example 5 RPA Using Rb69 Components

RPA reactions were established using Rb69 components, using primers J1 and K2 under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 100 ng/μl UvsX of Rb69, 20-100 ng/μl Rb69 UvsY, 400 ng/μl Rb69 gp32, 30 ng/μl Bsu polymerase, 7% Carbowax 20M, 300 nM amplification primers, 1:50,000 dilution from stock of SYBR green (Invitrogen). Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either no target (control—water) or 2500 copies of B. subtilis genomic DNA containing the target sequence. Samples contained varying concentrations of Rb69 UvsY, and the quantities used are indicated in the legend.

As shown in FIG. 14, positive signals developed in all samples during the 90 minute incubation, and the time of signal increase was earlier in the samples containing higher quantities of UvsY underlying an ideal requirement for concentrations of Rb69 UvsY of 60 ng/μl or over. The control sample was performed under identical conditions to the positive sample containing 60 ng/μl of UvsY, but lacking target DNA. This experiment shows that Rb69 components can be employed to configure a sensitive and specific amplification system.

Example 6 RPA Using Aeh1 Components

RPA reactions were established using Aeh1 components, using primers J1 (120 nM) and K2 (480 nM) under the following conditions: 50 mM Tris acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 200 ng/μl Aeh1 UvsX, 80 ng/μl Aeh1 UvsY, 500 ng/μl Aeh1 gp32, 30 ng/μl Bsu polymerase, 7% PEG compound, 120 nM fluorescent probe BsFlc. Exonuclease III was included at 65 ng/μl. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either water, 10, 100, or 1000 copies of B. subtilis genomic DNA containing the target sequence as indicated in the legend shown in FIG. 15.

Salt Titration

RPA reactions were also established using Aeh1 components testing salt titration, using primers J1 and K2 under the following conditions: 50 mM Tris.acetate pH XX, 60 or 80 or 100 or 120 or 140 or 160 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 150 ng/μl UysX of Aeh1, 50 ng/μl Aeh1 UvsY, 500 ng/μl Aeh1 gp32, 30 ng/μl Bsu polymerase, 7% Carbowax 20M, 300 nM amplification primers, 1:50,000 dilution from stock of SYBR green (Invitrogen). Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained 2000 copies of B. subtilis genomic DNA containing the target sequence.

As shown in FIG. 16, positive signals developed in all samples during the 90 minute incubation. This experiment suggests that Aeh1 components can be employed successfully to amplify DNA over a broad range of salt concentrations.

Aeh1 Compared to T4

RPA reactions were established to compare Aeh1 amplification to the T4 amplification system, using primers orfx45a (100 ng/μl) and sccii35IV (500 ng/μl) under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 200 ng/μl Aeh1 UvsX, 80 ng/μl Aeh1 UvsY, 500 ng/μl Aeh1 gp32, 70 ng/μl Bsu polymerase, 7% PEG Compound (Sigma), 120 nM fluorescent probe SATamra2, OR under similar conditions but with the following recombination components: 120 ng/μl T4 UvsX, 30 ng/μl T4 UvsY and 900 ng/μl T4 gp32. Exonuclease III was included at 65 ng/μl. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either water, 10 or 1000 copies of MRSA genomic DNA containing the target sequence as indicated in the legend. As shown in FIG. 17, no signals were detected with either recombination system when an estimated 10 copies had been provided. Based on later experiments it was believed that the DNA dilutions used for this experiment were compromised and hence that actual copy numbers were significantly lower than those expected. As shown in FIG. 17, the Aeh1 recombination system reaches detection threshold later than T4 and achieves a lower total signal strength in this experiment.

Aeh1 UvsX and UvsY can Amplify Using Heterologous gp32

RPA reactions were established using primers J1 and K2 under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 200 ng/μl UvsX of Aeh1, 100 ng/μl Aeh1 UvsY, 300 ng/μl Aeh1 gp32 OR 500 ng/μl Rb69 gp32 OR 700 ng/μl T4 gp32, 30 ng/μl Bsu polymerase, 7% Carbowax 20M, 300 nM amplification primers, 1:50,000 dilution from stock of SYBR green (Invitrogen). Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained 2000 copies of B. subtilis genomic DNA containing the target sequence.

As shown in FIG. 18, signals developed in all samples indicating that DNA amplification had occurred in all cases. The fastest and strongest signals developed when Aeh1 gp32 was employed, then Rb69 gp32, then T4 gp32. One should interpret the relative effectiveness of the gp32 molecules cautiously as they were not employed at the same concentrations.

Example 7 RPA Using Heterologous Reaction Components

RPA reactions were established using primers Apo300 and ApoB4 which amplify a roughly 300 base pair duplex product from human genomic DNA. The following conditions were employed: 50 mM Tris.acetate pH 8.3, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 200 ng/μl UvsX of KVP40, Aeh1 or Rb69, 32 ng/μl UvsY of KVP40, Aeh1 or T4 as indicated, 600 ng/μl Rb69 gp32 or T4 gp32, 30 ng/μl Bsu polymerase, 5% Carbowax 20M, 300 nM amplification primers. Reactions were established and left at 37° C. for 90 minutes. All samples contained 1000 copies of human genomic DNA containing the target sequence. The precise composition of each reaction with regard to species of gp32, UvsX and UvsY is indicated. Samples were cleaned by passage through a Qiagen PCR clean-up column and electrophoresed on a 2% agarose gel containing ethidium bromide. As shown in FIG. 19, amplification had occurred in the sample containing a heterologous mixture of Rb69 gp32 with Aeh1 UvsX and UvsY.

Example 8 Engineered Rb69 Constructs

Alterations to our parent clone of Rb69 UvsX in a modified pET21+ vector were engineered. The overall layout of the coding/primary amino acid sequence of RB69 drawing attention to regions of interest is shown at the top of the FIG. 20. Changes in the coding sequence were engineered, specifically to alter encoded amino acids in and around the Walker A motif, in and around the DNA-binding loop 2, and at the very C-terminus of the protein. Alterations in and around the Walker motif are as indicated by specific lettering and numeration referring to the position of the amino acid in the Rb69 wild-type protein, what the amino acid is, and to what it is mutated. For example H64S refers to alteration of histidine 64 of the native protein to a serine. Altered sequences in the region of DNA-binding loop 2 are indicated according to a different scheme. In this case most or all of the DNA binding loop sequences was replaced by the loop from T6 or T4 UvsX. When T6-1 is shown, this refers to replacement of the sequence NHT AMEIGGLYPKE IMG GG (SEQ ID NO:107) with the sequence NHT IETIEMFSKT VMG GG (SEQ ID NO:108), in which the underlined glycine is similar to the Rb69 sequences not the T6 native sequence. When T6 is shown, this refers to replacement of the Rb69 sequence with NHT IETIEMFSKT VMT GG (SEQ ID NO:109), in which the underlined threonine is the native T6 sequence in this position. When T4 is shown, this refers to replacement of the Rb69 sequence with the T4 sequence, that is NHT YETQEMFSKT VMG GG (SEQ ID NO:110). In the case of modifications to the C terminus the symbol ‘LSD’ indicates alteration of the native sequence of Rb69 at the very C terminus from the encoded amino acid sequence END LDE MEDFDE (SEQ ID NO:111) to the sequence END LDE LSD MEDFDE (SEQ ID NO:112). The symbol ‘LDE LDE’ or sometimes in the legends ‘2xLDE’ refers to changing the Rb69 C-terminal sequence to END LDE MEDFDE LDE LDE (SEQ ID NO:113). Note that in all cases the very C-terminal sequence is followed by 18 bases encoding 6 histidine residues that are used for protein purification.

Briefly, selected sequences discussed above are listed below.

The Rb69 UvsX H64S sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKSFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAINHTAMEI GGLYPKEIMG GGTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE (HHHHHH) (SEQ ID NO:114). The six “H” at the end is optional.

The Rb69 UvsX H64S LSD sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKSFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAINHTAMEI GGLYPKEIMG GGTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE LSD (HHHHHH) (SEQ ID NO:115). The six “H” at the end is optional.

The Rb69 UvsX H64S 2xLDE sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKSFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAINHTAMEI GGLYPKEIMG GGTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE LSD LDELDE (HHHHHH) (SEQ ID NO:116). The six “H” at the end is optional.

The Rb69 UvsX H64S T6/2xLDE sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKSFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAINHTIETI EMFSKTVMTG GTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE LSD LDELDE (HHHHHH) (SEQ ID NO:117). The six “H” at the end is optional.

The Rb69 UvsX H64S T4/2xLDE sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKSFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAINHTYETQ EMFSKTVMGG GTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE LSD LDELDE (HHHHHH) (SEQ ID NO:118). The six “H” at the end is optional.

The Rb69 UvsX H64S T67S L68N T4/2xLDE sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKSFKSNFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAINHTYETQ EMFSKTVMGG GTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE LSD LDELDE (HHHHHH) (SEQ ID NO:119). The six “H” at the end is optional.

Additional alterations to the parent clone of Rb69 UvsX in a modified pET21+ vector were generated. The overall layout of the coding/primary amino acid sequence of Rb69 drawing attention to additional regions of interest is shown at the top of the FIG. 21. Changes in the coding sequence were engineered, specifically in and around the DNA-binding loop 2. The entire DNA-binding loop2 sequence was replaced with the equivalent sequences from phage 133, phage Aeh1, phage KVP40, a representative (hybrid) cyanophage sequence, or the loop from E. coli RecA. A loop which was part Aeh1 and part Rb16 was also tested. The precise amino acid substitutions are indicated in FIG. 21. A summary remark regarding the behaviour/activity of the protein produced from these clones during expression/purification or testing in RPA is given on the left of FIGS. 20 and 21.

The Rb69 UvsX sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKHFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAINHTAMEI GGLYPKEIMG GGTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE (SEQ ID NO:120)

The Rb69 Loop133 UvsX sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKHFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAI NHT LQTLEMFSKEVMT GGTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE (SEQ ID NO:121)

The Rb69 LoopKVP40 UvsX sequence is as follows: MSDLKSRLIK ASTSKMTADL TKSKLFNNRD EVPTRIPMLN IALGGALNAG LQSGLTIFAA PSKHFKTLFG LTMVAAYMKK YKDAICLFYD SEFGASESYF RSMGVDLDRV VHTPIQSVEQ LKVDMTNQLD AIERGDKVII FIDSIGNTAS KKETEDALNE KVVGDMSRAK ALKSLFRIVT PYLTIKDIPC VAI NHT YQTQEWSKTVMS GGTGILYSAN TVFFISKRQV KEGTELTGYD FTLKAEKSRT VKEKSTFPIT VNFDGGIDPF SGLLEMATEI GFVVKPKAGW YAREFLDEET GEMIREEKSW RAKATDCVEF WGPLFKHKPF RDAIETKYKL GAISSIKEVD DAVNDLINCK ATTKVPVKTS DAPSAADIEN DLDEMEDFDE (SEQ ID NO:122)

Activity of Rb69 H64S

A kinetic study of the activity of mutant Rb69 H64S protein compared to wild type Rb69, or T4 UvsX, was made. A fluorescent probe based monitoring approach was taken. General conditions were as for the experiment shown in FIG. 13 with the exception of the type and concentrations of recombination components, and that PEG compound was employed at 7% w/v. Other changes are as follows: 120 ng/μl T4 UvsX, 900 ng/μl T4 gp32, 50 ng/μl T4 UvsY, OR 100 ng/μl Rb69 or Rb69 H64S UvsX, 400 ng/μl Rb69 gp32, 80 ng/μl Rb69 UvsY. Target DNA was present at 100 copies total. As shown in FIG. 22, the Rb69 H64S protein works well according to this assay (although this experiment does not address the nature of the DNA generated during amplification) and seems to outperform the kinetics of the wild-type protein. In the next experiment performed the rate under apparently identical conditions (400 ng/μl Rb69 gp32) the outcome was slightly different. This is most likely due to slight pipetting errors in the latter experiment.

Rb69 H64S—Relative Resistance to gp32 Up-Titration

A kinetic study of the activity of mutant Rb69 H64S protein compared to wild type Rb69 was made in which the quantity of Rb69 gp32 was varied somewhat. A fluorescent probe based monitoring approach was taken. General conditions were as for the experiment shown in FIG. 22 with the exception of a variable concentration of gp32 protein, and that PEG compound was employed at 6% w/v. Conditions were: 100 ng/μl Rb69 or Rb69 H64S UvsX, Rb69 gp32 concentration as indicated, 80 ng/μl Rb69 UvsY. Target DNA was present at 100 copies total. As shown in FIG. 23, up-titration of gp32 had less impact on kinetics of Rb69 H64S compared to Rb69 protein. It was concluded that RbH64S is somewhat more resistant to competition by gp32.

Activity of Rb69 H64S Compared to Wild Type Rb69

A kinetic study of the activity of mutant Rb69 H64S protein compared to wild type Rb69 was made. A fluorescent probe based monitoring approach was taken. General conditions were as for the experiment shown in FIG. 22 with the exception of the type and concentrations of recombination components, and that PEG compound was used at 6% w/v. Other conditions are as follows: 100 ng/μl Rb69 or Rb69 H64S UvsX, 400 ng/μl Rb69 gp32, 80 ng/μl Rb69 UvsY. Target DNA was present at 0 copies, 100 copies, or 1000 copies total as indicated. As shown in FIG. 24, the Rb69 H64S protein works well according to this assay and outperforms the behaviour of the wild-type protein.

Activity of Rb69 UvsX H64S at 300-500 ng/μl gp32

A kinetic study of the activity of mutant Rb69 H64S protein was made under conditions of 300, 400, or 500 ng/μl of Rb69 gp32 protein. A fluorescent probe based monitoring approach was taken. General conditions were as for the experiment shown in FIG. 22 but gp32 concentrations were varied and PEG compound was used at 6% w/v. Protein concentrations were thus as follows: 100 ng/μl Rb69 H64S UvsX, 300-500 ng/μl Rb69 gp32, 80 ng/μl Rb69 UvsY. Target DNA was present at 0 (water control) or 100 copies total as indicated. As shown in FIG. 25, the Rb69 H64S protein works well according to this assay with little difference in kinetic behaviour over the tested range of Rb69 gp32 protein.

Titration of Rb69 UvsX H64S

A kinetic study of the activity of mutant Rb69 H64S UvsX protein was made under varying concentrations of UvsX protein. A fluorescent probe based monitoring approach was taken. General conditions were as for the experiment shown in FIG. 22 but the concentration of Rb69 H64S UvsX was varied and PEG compound was used at 6% w/v. Protein concentrations were thus as follows: 100, 150 or 200 ng/μl Rb69 H64S UvsX, 500 ng/μl Rb69 gp32, 80 ng/μl Rb69 UvsY. Target DNA was present at 0 (water control) or 100 copies total as indicated. As shown in FIG. 26, the Rb69 H64S protein works well according to this assay providing that the UvsX concentration does not significantly exceed 100 ng/μl.

Another kinetic study of the activity of mutant Rb69 H64S protein was performed under varying concentrations of UvsX protein using a fluorescent probe based monitoring approach. General conditions were as for the experiment shown in FIG. 22 but the concentration of Rb69 H64S UvsX was varied and PEG compound was employed at 6% w/v. Protein concentrations were thus as follows: 60, 80 or 100 ng/μl Rb69 H64S UvsX, 500 ng/μl Rb69 gp32, 80 ng/μl Rb69 UvsY. Target DNA was present at 0 (water control) or 100 copies total as indicated. As shown in FIG. 27, the Rb69 H64S protein works well according to this assay regardless of whether the protein was in the range 60-100 ng/μl.

Effectiveness of Rb69 gp32 in Reactions with T4 UvsX and UvsY

A kinetic study investigating the utility of Rb69 gp32 when combined with T4 UvsX and UvsY was performed. RPA reactions were established using primers J1 (120 ng/μl) and K2 (480 ng/μl) under the following conditions: 50 mM Tris. acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 120 ng/μl T4 UvsX, 30 ng/μl T4 UvsY, 900 ng/μl T4 gp32 OR 500 ng/μl Rb69 gp32 OR 1000 ng/μl, 30 ng/μl Bsu polymerase, 6% PEG 35,000, 120 nM fluorescent probe BsFlc. Exonuclease III was included at 65 ng/μl. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either water or 100 copies of B. subtilis genomic DNA containing the target sequence as indicated in the legend. As shown in FIG. 28, all template positive samples worked effectively and there appeared to be little difference between using T4 and Rb69 gp32 protein.

T4 Outperforms Rb69 UvsX/UvsY System when Rb69 gp32 is Used in Both Cases

A kinetic study investigating the utility of Rb69 gp32 when combined with T4 UvsX and UvsY, or when combined with Rb69 UvsX and UvsY. RPA reactions were established using primers J1 (120 nM) and K2 (480 nM) under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 120 ng/μl T4 UvsX, 30 ng/μl T4 UvsY, 1000 ng/μl Rb69 gp32, 30 ng/μl Bsu polymerase, 6% PEG 35,000, 300 nM amplification primers, 120 nM fluorescent probe BsFlc. Exonuclease III was included at 65 ng/μl. Alternatively similar conditions were employed but the recombinase was 100 ng/μl Rb69 UvsX and the loading protein was 80 ng/μl Rb69 UvsY protein. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either water or 100 copies of B. subtilis genomic DNA containing the target sequence as indicated in the legend. As shown in FIG. 29, all template positive samples developed positive signals, however the system established with T4 UvsX and UvsY develop much earlier and stronger signals. It was concluded that when the Rb69 gp32 concentration is raised to 1000 ng/μl Rb69 little inhibition of amplification occurs when the T4 components are used, but when Rb69 UvsX and UvsY are used there is significant inhibition (see effects of Rb69 gp32 overtitration with Rb69 UvsX and UvsY in FIG. 23).

Poor Activity of Rb69 UvsX H64T Protein

An RB69 UvsX-encoding clone was generated in which histidine 64 was altered to a threonine. This mutation was analogous to the Rb69 UvsX H64S protein assessed earlier, and was designed to test whether a threonine residue would be as effective as a serine residue at improving RPA behaviour. General reaction conditions were the same as described for the experiment in FIG. 29 with the following exceptions: UvsX was either Rb69 wild type UvsX at 100 ng/μl or Rb69 UvsX H64T at 100 ng/μl, Rb69 UvsY at 80 ng/μl, and 500 ng/μl Rb69 gp32. DNA target was present either at 0 or 100 copies. As shown in FIG. 30, reactions performed using Rb69 UvsX H64T barely developed signal and it was deduced that this amino acid substitution is not effective in contrast to when a serine is substituted at this position.

ATP Titration Using Rb69 UvsX

The effects of different ATP concentrations on the amplification kinetics when using Rb69 UvsX protein were investigated. Reaction conditions were as in FIG. 30 but only wild-type Rb69 gp32, UvsX, and UvsY were used. The final concentration of ATP was adjusted to either 1 mM, 2 mM, or 3 mM. Target was present at either 0 or 100 copies as indicated. As shown in FIG. 31, amplification occurred in all cases that target DNA was present, but the strongest signals develop when 3 mM ATP is used.

Suppressing Effect of T4 gp32 on Rb69 UvsX and UvsY

The effects using T4 gp32 protein with Rb69 UvsX and UvsY proteins were investigated. Conditions were the same as those described in FIG. 29 with the following modifications. Rb69 UvsX was used at 100 ng/μl, Rb69 UvsY was used at 80 ng/μl, and gp32 was either Rb69 gp32 at 500 ng/μl OR T4 gp32 at 500 ng/μl OR T4 gp32 at 1000 ng/μl. As shown in FIG. 32, signals only develop when Rb69 gp32 is used, and not when T4 gp32 is employed contrasting with the full compatibility of Rb69 gp32 when used with T4 heterologous components.

Consequences of Modification to the C Terminus of Rb69 UvsX

A kinetic analysis of amplification reactions configured with Rb69 UvsX H64S, with Rb69 UvsX H64S LSD, and with Rb69 UvsX H64S 2xLDE was performed. General reaction conditions were as described in FIG. 29, except that different UvsX proteins were used in all cases at 100 ng/μl. Rb69 UvsY was used at 80 ng/μl. Rb69 gp32 was used at 500 ng/μl. DNA target was present at either 0 or 1000 copies. As shown in FIG. 33, strong signals develop in all target-containing samples and show similar kinetics. A very slight tendency for the proteins with more acidic C-termini (LSD and 2xLDE clones) to initiate signal very slightly later and to generate slightly stronger signals in total is seen.

A similar experiment to that described in FIG. 33 was performed. However in this case DNA target was present at either 0 or 100 copies. As shown in FIG. 34, strong signals develop in all target-containing samples and show, once again, fairly similar kinetics. In this case, a slightly stronger tendency for the proteins with more acidic C-termini (LSD and 2xLDE clones) to initiate signal slightly later and to generate stronger signals was observed.

Titration of PEG When Using Rb69 UvsX H64S/2xLDE

Similar conditions were employed as in the experiment described in FIG. 33. However in this case only Rb69 UvsX H64S 2xLDE was used and at a concentration of 100 ng/μl, Rb69 UvsY was used at 80 ng/μl, and Rb69 gp32 was used at 500 ng/μl. DNA target was present at either 0 or 200 copies per reaction as indicated. The concentration of polyethylene glycol (M.W. 35,000 Fluka) was tested at 5%, 6%, and 7%. As shown in FIG. 35, the best signals were obtained when polyethylene glycol M.W. 35,000 was used at 5% w/v.

Example 9 Engineered UvsY Constructs

A schematic representation is shown of the peptide sequence predicted to be encoded by the T4 UvsY and Rb69 UvsY genes is shown in FIG. 36. Residues that are substituted between these 2 proteins are indicated, all other residues are identical. Two chimeric clones which were used to express chimeric proteins were generated. Each chimera consisted of the N-terminal half of one UvsY molecule fused to the C-terminal half of the other. These are termed UvsY hybrid 1 and UvsY hybrid 2.

Activity of UvsY Hybrids with T4 UvsX and T4 gp32

An experiment was performed to address how well the T4, Rb69, and hybrid UvsY proteins described in FIG. 36 would function when combined with T4 UvsX and T4 gp32.

Standard conditions as described for the experiment in FIG. 29 were used but with the following modifications. T4 UvsX was employed at a concentration of 120 ng/μl, T4 gp32 was employed at 900 ng/μl, and the UvsY proteins tested were used at 80 ng/μl. DNA target was present at either 0 or 1000 copies in each reaction. PEG 35,000 (Fluka) was employed at 5% w/v. As shown in FIG. 37, all of the different forms of UvsY behaved excellently in this assay indicating that when T4 UvsX and T4 gp32 are employed there is little or no preference visible for T4 vs Rb69 UvsY, nor any significant distinction from the hybrid molecules.

Activity of UvsY Hybrids with Rb69 UvsX and Rb69 gp32

An experiment was performed to address how well the T4, Rb69, and hybrid UvsY proteins described in FIG. 36 would function when combined with Rb69 UvsX and Rb69 gp32. Standard conditions as described for the experiment in FIG. 37 were used but with the following modifications. Rb69 UvsX H64S 2xLDE was employed at a concentration of 100 ng/μl, Rb69 gp32 was employed at 500 ng/μl, and the UvsY proteins tested were used at 80 ng/μl. DNA target was present at either 0 or 1000 copies in each reaction. As shown in FIG. 38, all the forms of UvsY functioned in this assay, however there were strong differences in response time and signal strength. This indicates that when Rb69 UvsX and RB69 gp32 are employed there is a clear preference for Rb69 UvsY.

The sequence of UvsY hybrid 1 is as follows: HHHHHHMRLEDLQEEL KKDVFIDSTK LQYEAANNVM LYSKWLNKHS SIKKEMLRIE AQKKVALKAR LDYYSGRGDG DEFSMDRYEK SEMKTVLAAD KDVLKIETTL QYWGILLEFC SGALDAVKSR SFALKHIQDM REFEAGQ (SEQ ID NO:123). The N terminus six histidines are optional.

The sequence of UvsY hybrid 2 is as follows: HHHHHHMKLEDLQEEL DADLAIDTTK LQYETANNVK LYSKWLRKHS FIRKEMLRIE TQKKT ALKAR LDYYSGRGDG DEFSMDRYEK SEMKTVLSAD KDVLKVDTSL QYWGILLDFC SGALDAIKSR GFAIKHIQDM RAFEAGK (SEQ ID NO:124). The N terminus six histidines are optional.

Example 10 Additional Analysis of Rb69 Engineered Constructs and Chimeras

No Activity for Rb69 UvsX H64S/T6-1/2xLDE

The activity of Rb69 UvsX H64S/T6-1 2xLDE in comparison to the robust activity of Rb69 UvsX H64S/2xLDE was investigated. Reactions were established according to standard conditions described in FIG. 29 with the following modifications. Rb69 UvsX H64S/2xLDE protein and Rb69 UvsX H64S/T6-1/2xLDE protein were used at 100 ng/μl, Rb69 gp32 was used at 600 ng/μl, and Rb69 UvsY was employed at 80 ng/μl. DNA target was present at either 0 or 1000 copies per reaction. As shown in FIG. 39, robust activity was exhibited by the Rb69 UvsX H64S/2xLDE protein, but no activity was detected with Rb69 UvsX H64S/T6-1/2xLDE protein. Apparently recoding the DNA-binding loop 2 sequence in this case resulted in a non-functional protein.

Titration of Rb69 gp32 in the Presence of Rb69 UvsX H64S/2xLDE

The effects of titrating Rb69 gp32 protein on amplification kinetics when employing the Rb69 UvsX/H64S 2xLDE protein were investigated. Reactions were established according to standard conditions described in FIG. 29 with the following modifications. PEG 35,000 (Fluka) was used at 5% w/v. Rb69 UvsX H64S/2xLDE protein was used at 100 ng/μl, Rb69 gp32 was used at 400, 700, or 1000 ng/μl, and Rb69 UvsY was employed at 80 ng/μl. DNA target was present at either 0 or 100 copies per reaction. As shown in FIG. 40, increasing quantities of Rb69 gp32 lead to a delay in onset of signal detection.

No activity for Rb69 UvsX H64S/F69M/G70S/T6-1/2xLDE

The effects of using Rb69 UvsX H64S/F69M/G70S/T6-1/2xLDE protein in amplification reactions were investigated. This clone was similar to that tested earlier containing most of the T6 UvsX DNA-binding loop 2, but also contained 2 additional T6-like residues near to the Walker A motif Reactions were established according to standard conditions described in FIG. 40 with the following modifications. Rb69 UvsX H64S/2xLDE protein or Rb69 UvsX H64S F69M/G70S/T6-1/2xLDE were used at 100 ng/μl, Rb69 gp32 was used at 500 ng/μl, and Rb69 UvsY was employed at 80 ng/μl. DNA target was present at either 0 or 1000 copies per reaction. As shown in FIG. 41, no activity is detected for the Rb69 UvsX H64S F69M/G70S/T6-1/2xLDE protein.

Strong Activity of Rb69 H64S T67S/L68N/T4/2xLDE and Rb69 H64S/T4/2xLDE

The effects of using Rb69 H64S T67S/L68N/T4/2xLDE and Rb69 H64S/T4/2xLDE protein in amplification reactions were investigated. These proteins were analogous to those tested earlier containing T6 UvsX DNA-binding loop 2 and/or additionally containing T6-like residues near to the Walker A motif, except that in this case the DNA-binding loop2 sequences and Walker A sequences were derived from T4 UvsX (see clone schematic chart). Reactions were established according to standard conditions described in FIG. 40 with the following modifications. Rb69 UvsX protein or Rb69 UvsX H64S/2xLDE or Rb69 UvsX H64S/T67S/L68N/T4/2xLDE were used at 100 ng/μl, Rb69 gp32 was used at 500 ng/μl, and Rb69 UvsY was employed at 80 ng/μl. DNA target was present at either 0 or 100 copies per reaction. As shown in FIG. 42, excellent activity was detected for all UvsX proteins tested indicating that the T4 DNA-binding loop and associated Walker A residues may be substituted successfully into the Rb69 UvsX protein.

Rb69 UvsX H64S/T67S/L68N/T4/2xLDE Protein is Relatively Resistant to Up-Titration of Rb69 gp32

The inhibitory effect of overtitration of Rb69 gp32 on reaction kinetics comparing wild-type Rb69 UvsX and Rb69 UvsX H64S/T67S/L68N/T4/2xLDE was investigated. Reactions were established according to standard conditions described in FIG. 40 with the following modifications. Rb69 UvsX protein or Rb69 UvsX H64S/T67S/L68/T4/2xLDE were used at 100 ng/μl, Rb69 gp32 was used at either 400 or 800 ng/μl, and Rb69 UvsY was employed at 80 ng/μl. DNA target was present at either 0 or 100 copies per reaction. As shown in FIG. 43, the slowing in time to detection experienced for Rb69 UvsX H64S/T67S/L68N/T4/2xLDE compared to wild-type Rb69 UvsX when increasing the gp32 concentration was only about half as much. It was concluded that the substituted protein is less sensitive to gp32 concentration.

Rb69 UvsX H64S/T67S/L68N/T4/2xLDE Protein can Function with T4 gp32

Whether or not the inhibitory effect of T4 gp32 on reactions configured with Rb69 UvsX and UvsY could be overcome by the use of Rb69 UvsX H64S/T67S/L68N/T4/2xLDE was investigated. Reactions were established according to standard conditions described in FIG. 40 with the following modifications. T4 UvsX protein or Rb69 UvsX or Rb69 UvsX H64S/T67S/L68N/T4/2xLDE were used at 120 ng/μl or 100 ng/μl or 100 ng/μl respectively, T4 gp32 was used at 700 ng/μl, and T4 or Rb69 UvsY was employed at 30 ng/μl or 80 ng/μl respectively. T4 UvsX was combined with T4 UvsY, and the Rb69 UvsX proteins were combined with Rb69 UvsY. DNA target was present at either 0 or 100 copies per reaction. As shown in FIG. 44, Rb69 UvsX H64S/T67S/L68N/T4/2xLDE functioned almost as well as the T4 components, while wild-type Rb69 UvsX was inactive when T4 gp32 was used. It was concluded that the substituted Rb69 protein has developed very good tolerance to T4 gp32.

Rb69 UvsX Chimeras Containing DNA-Binding Loops from Phage 133 Work Weakly, while Cyanophage and Aeh1 Loops are Non-Functional

The activity of Rb69 UvsX proteins in which the DNA-binding loop2 had been replaced with sequences found in other diverse UvsX-like molecules was investigated. Reactions were established according to standard conditions described in FIG. 40 with the following modifications. Rb69 UvsX protein or Rb69 UvsX loop 133 or Rb69 loop Cyano or Rb69 loop Aeh1 were used at 100 ng/μl, Rb69 gp32 was used at either 500 ng/μl, and Rb69 UvsY was employed at 80 ng/μl. As shown in FIG. 45, no activity was detected for the proteins containing cyanophage or Aeh1 loops, while the protein containing the Phage 133 loop showed very weak activity.

Rb69 UvsX H64S/T6/2xLDE is Active Unlike the Equivalent Lacking the Final G to T Substitution of the DNA-Binding Loop2

The activity of Rb69 UvsX H64S/T6/2xLDE was tested, that is a protein in which the final residue that differs between T4 and T6 has been altered to the T6 equivalent unlike the case with Rb69 UvsX H64S T6-1 2xLDE. Also tested was a protein in which the DNA-binding loop2 had been replaced with a hybrid of the Aeh1 loop and the Rb16 loop (possessing the unusual alanine at the beginning of the Aeh1 loop instead of the cysteine found in Rb16) Reactions were established according to standard conditions described in FIG. 40 with the following modifications. Rb69 UvsX protein or Rb69 UvsX H64S/T6/2xLDE or Rb69 loop (hybrid Aeh1/Rb16) were used at 100 ng/μl, Rb69 gp32 was used at either 500 ng/μl, and Rb69 UvsY was employed at 80 ng/μl. As shown in FIG. 46, no activity was detected for the proteins containing the Aeh1/Rb16 hybrid loop, however the protein containing the repaired T6 loop showed excellent activity. It was concluded that a complete replacement of the T6-like DNA-binding loop 2 results in activity, but hybrids of the similar T4 and T6 loops are not active indicating that substitutions between T4 and T6 are not silent and must be exchanged in groups.

Example 11 Manganese Ions are Able to Support RPA Reactions

RPA reactions were established under the following conditions: 50 mM Tris. acetate pH8.3, 100 mM Potassium acetate, 200 μM dNTPs, 3 mM ATP, 50 mM phosphocreatine, 120 ng/μl T4 UvsX, 30 ng/μl T4 UvsY, 900 ng/μl T4 gp32, 5% PEG 35,000, 30 ng/μl Bsu polymerase, 1000 copies B. subtilis genomic DNA. Divalent manganese cations were supplied individually to each reaction to give final concentrations of 0.1 mM, 0.5 mM, 1 mM, 2 mM, 3 mM. Alternatively as a control 16 mM Magnesium was employed. Reactions were incubated at 37° C. for 90 minutes, purified on PCR clean-up columns (SIGMA) and then separated on a 2% agarose gel before visualization with ethidium bromide. As shown in FIG. 47, manganese ions efficiently supported RPA in the concentration range of 0.5 to 3 mM manganese. Significantly higher concentrations (from about 4-5 mM Manganese—not shown here) started to inhibit reactions behaviour which lead to progressively less product until at 10 mM manganese no product was detected with these primers after 90 minutes. Some carry-over of magnesium ions from buffers is anticipated, perhaps accounting for roughly 0.5 mM magnesium ions total per reaction.

Example 12: Staphylococcus aureus Polymerase I Large Fragment Functions Well in RPA Reactions

RPA reactions were configured using alternative polymerases capable of strand displacement synthesis, including bacterial polymerase I repair enzymes which bear homology to the Pol I class of E. coli, Bacillus subtilis, and Staphylococcus aureus. In this experiment, either the Bacillus subtilis PolI large fragment described elsewhere and herein, or with the equivalent large fragment from S. aureus, generated in-house were used in RPA reactions. Reactions were configured under standard conditions, namely: 300 nM primer J1, 300 nM primer K2, 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 200 μM dNTPs, 3 mM ATP, 50 mM phosphocreatine, 120 ng/μl T4 UvsX, 30 ng/μl T4 UvsY, 900 ng/μl T4 gp32, 5% PEG compound (SIGMA), 70 ng/μl Bsu polymerase OR 70 ng/μl S. aureus (Sau) polymerase, and 0, 100, 1000 or 10,000 copies B. subtilis genomic DNA. Reactions were monitored by the inclusion of 1:50,000 dilution of SYBR green (Invitrogen). As shown in FIG. 48, iboth cases robust amplification occurred. If anything the temporal separation between water and target-containing samples was larger when S. aureus polymerase was employed. This could indicate that this polymerase displays slightly improved characteristics for sensitive RPA reactions.

Example 13 Use of Heparin in RPA Reactions Heparin Slows the Development of Signals in Zero-Target Controls

RPA reactions were configured using the J1 and K2 primers used elsewhere in this disclosure but deliberately omitted target DNA. Reactions were configured under standard conditions, namely: 300 nM primer J1, 300 nM primer K2, 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 200 μM dNTPs, 3 mM ATP, 50 mM phosphocreatine, 120 ng/μl T4 UvsX, 30 ng/μl T4 UvsY, 900 ng/μl T4 gp32, 5% PEG compound (SIGMA), 30 ng/μl Bsu polymerase. Reactions were monitored by the inclusion of 1:50,000 dilution of SYBR green (Invitrogen). Heparin was either not included in the reaction, or present at 20 ng/μl. As shown in FIG. 49, after some time background signals develop in all reactions, however this occurs later for those samples containing heparin suggesting it slows noise development.

Heparin Improves Signal: Noise Ratios in RPA Reactions

A kinetic study was made to investigate the effects of heparin on the sensitivity and kinetics of amplification reactions monitored via a probe-based approach. RPA reactions were established using primers J1 (120 ng/μl) and K2 (480 ng/μl) under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 120 ng/μl T4 UvsX, 30 ng/μl T4 UvsY, 1000 ng/μl Rb69 gp32, 30 ng/μl Bsu polymerase, 5% PEG compound, 120 nM fluorescent probe BsFlc. Exonuclease III was included at 65 ng/μl. Heparin was either absent or present at 20 ng/μl as indicated. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38° C. at which time measurements were taken periodically from a bottom-reading probe. Samples contained either water, 10, 100, 1000 or 10,000 copies of B. subtilis genomic DNA containing the target sequence as indicated in the legend. As shown in FIG. 50, all template positive samples developed positive signals, however the system established with heparin showed improvement in the consistency of signal development at 10 copies It was concluded that the heparin inclusion slowed noise development which lead to less of a breakdown of simultaneity of signal detection at low copy numbers.

Example 14 3′-Blocked Primers and E. coli Exonuclease III in RPA Reactions

Strong evidence was discovered which suggests that primers which were 3′-blocked with groups such as biotin, via a carbon-oxygen-carbon linkage at least, may be successfully employed as amplification primers if E. coli exonuclease III is included in the reaction. This experiment provides an example of this phenomenon. In this experiment RPA reactions were performed by amplifying a fragment from the Bacillus subtilis genome using the primers J1 and K2 used widely in this document. The use of a primer designated K2-epsilon which had been designed for other purposes. This primer has the same sequence as the K2 primer, but differs in its possession of a 3′-blocking biotin group which is attached via a linker and described as biotin-TEG (see suppliers website http://uk.eurogentec.com). This constitutes a biotin attached via a linker which is joined to the 3′ sugar via an oxygen atom. The K2-epsilom primer also contains a deoxyuracil residue replacing a deoxythymidine residue within the body of the sequence, however this is considered of no relevance to this experiment. Reactions contained the J1 primer paired with the K2 primer OR the K2-epsilon ‘blocked’ primer, and either exonuclease III or E. coli Nfo protein. RPA reactions were established using primers J1 (120 ng/μl) and K2 or K2 epsilon (480 ng/μl) under the following conditions: 50 mM Tris.acetate pH 7.9, 100 mM Potassium acetate, 14 mM Magnesium acetate, 50 mM Creatine phosphate (Calbiochem), 3 mM ATP (Roche), 200 micromolar dNTPs, 50 ng/μl creatine kinase (Roche), 120 ng/μl T4 UvsX, 30 ng/μl T4 UvsY, 1000 ng/μl T4 gp32, 30 ng/μl Bsu polymerase, 5% PEG compound, 120 nM fluorescent probe BsFlc.

Exonuclease III was included at 65 ng/μl or endonuclease IV (Nfo) was included at 200 ng/μl. Despite the blocked nature of the K2 epsilon primer, when exonuclease III is used as the agent to process the probe to generate fluorescence, there is no difference in amplification kinetics between samples employing K2 and those employing K2-epsilon, as shown in FIG. 51. This suggests that exonuclease III rapidly processes non-extendable hybrids of template bound to K2-epsilon into extendable forms, presumably either by exonuclease activity or via the 3′-diesterase or phosphatase types of activity that have been attributed to this enzyme and Nfo (also known as endonuclease IV). In contrast, when Nfo was employed in place of Exo III, there was a general delay in amplification but this was much more marked for the J1 paired with K2-epsilon reaction. It was concluded that the ‘activation’ process works poorly when Nfo is employed, but very rapidly when exoIII is employed.

Example 15 UvsY-Free DNA Amplification

A series of experiments were performed to investigate the effects on DNA amplification by removing UvsY from the RPA reaction.

UvsY-Free DNA Amplication Using T6 H66S

In this experiment RPA was performed under the following conditions: 100 mM Potassium acetate, 50 mM Tris.acetate pH 8.3, 14 mM Magnesium acetate, 5 mM dTT, 200 mM dNTPs, 50 mM Creatine phosphate (Calbiochem), 2.5 mM ATP (Roche), 50 ng/μl Creatine Kinase (Roche), 300 nM amplification primers, 5% PEG 35,000, 43 ng/μl S.au Polymerase, 600 ng/μl Rb69 gp32, 120 ng/μl T6 H66S UvsX and 79 ng/μl Rb69 UvsY, where appropriate. Reactions were carried out using 1000 copies MS2 DNA template with primer MS2 downRT2 and primer MS2 up4, up5, up6 or up7, and in the presence or absence of Rb69 UvsY. Reactions were established on ice and then transferred to 37° C. for 1 hour. Following amplification, the products were purified using the GenElute PCR cleanup kit (Sigma) and visualised using gel electrophoresis. Discovered unexpectedly was that T6 H66S recombinase could effectively amplify DNA in RPA reactions in the absence of UvsY. As shown in FIG. 52, products of the correct size were amplified in the presence of UvsY. In the absence of UvsY, with the exception of the MS2 downRT2+MS2 up5 reaction products, the most abundant product appeared to be of the same size as that synthesised when UvsY is present. It was concluded that, with the template and primer pairs used, RPA DNA amplification is possible in the absence of UvsY and that such reactions often produce products of the correct size.

An additional experiment was carried out to explore whether the UvsY-independent amplification observed previously would occur using different primer pairs synthesising different sized products. The results for this additional experiment exquisitely show just how effective amplification can be using the T6 H66S recombinase in the absence of UvsY (although kinetics are not investigated). General reaction conditions were the same as described in for the experiment depicted in FIG. 52, with the following exceptions: reactions were carried out using primer MS2 down5 with primer MS2 up5, up6, up7 or up2. Reactions were also carried out using primers MS2 down2 and MS2 up4. Amplification products were made when using any of the primer combinations and in both presence and absence of UvsY. As shown in FIG. 53, all reactions worked well except with the MS2 down5/up5 primer pair, although this still produced a small amount of the correct product. The major product from each reaction was of the correct size regardless of whether UvsY was present in the reaction or not. In the absence of UvsY there appeared to be a greater abundance of incorrect products, however these were present in lower amounts than the correct product. It was concluded that different sized RPA products can be amplified using a variety of primer pairs and that the ability of the reaction to proceed in the absence of UvsY is unlikely to be dependent upon the primers used or the resultant product size.

UvsY-Free Amplification of Small Genomic DNA Targets

A study was performed to investigate whether, in the absence of UvsY, the size of the DNA target plays a role in the ability of RPA to amplify DNA. To this end, a small 305 bp RPA product, amplified from human genomic DNA, was used as the DNA target in an RPA reaction. Reaction conditions were the same as stated for the experiment depicted in FIG. 52, with the exception that the reactions were carried out using 1000 copies of DNA target with primer ApoB4 and either primer ApoB300, ApoB3, ApoB7 or ApoB10, which generate products of 305 bp, 210 bp, 143 bp and 141 bp, respectively. As shown in FIG. 54, in the absence of UvsY all of the reactions generated DNA amplicons, however despite an apparently robust capability to synthesise DNA products in the absence of UvsY, products generated using T6 H66S UvsX without UvsY were not always those of the expected size and the same size as those produced in the presence of UvsY. Presumably primer-related artefacts are sometimes dominant to bona fide product formation, although the reasons are unclear. It was concluded that in the absence of UvsY, DNA amplification occurs reasonably proficiently using a small DNA target but unlike when UvsY is present, the product is always of the correct size.

UvsY Free Amplification of Complex Genomic Targets

This experiment addressed whether low copy numbers of complex genomic targets may be amplified in the absence of UvsY. Reaction conditions were the same as described for the experiment depicted in FIG. 52, with the exception that reactions were carried out using 1000 copies of human genomic DNA with primer ApoB4 and either primer ApoB300, ApoB3, ApoB7 or ApoB10, which generate products of 305 bp, 210 bp, 143 bp and 141 bp, respectively. As shown in FIG. 55, in the absence of UvsY, DNA amplification occurred for all reactions, however the products generated using T6 H66S UvsX without UvsY were not always those of the expected size and the same size as those produced in the presence of UvsY. It was concluded that in the absence of UvsY, DNA amplification occurs efficiently using a complex genomic DNA target but unlike reactions performed in the presence of UvsY, where the correct product is usually synthesised, the product is always of the correct size.

UvsY Free DNA Amplification Requires PEG

An experiment was performed to address whether the UvsY-independent behaviour exhibited by T6 H66S recombinase extended further to a lack of requirement for PEG. These reactions were conducted as described for the experiment depicted in FIG. 52, with the following exceptions: reactions were performed using 1000 copies of human genomic DNA and primer ApoB4 with either primer ApoB300 or ApoB3, both with and without the presence of PEG. As shown in FIG. 56, the results demonstrated a stark difference in reaction productivity between when PEG is present or absent. This experiment demonstrated the criticality of the use of polyethylene glycol inclusion in RPA reactions to permit effective amplification. In the absence of PEG, amplification of bona fide products generally does not occur, although a very faint artifact may be present in one lane, perhaps indicating a low level of loaded filaments when the T6 H66S recombinase is employed (although this does not occur in the presence of UvsY). It was concluded that for correct and effective amplification of target DNA, regardless of the presence or absence of UvsY, PEG is necessary in the reaction.

UvsY-Free DNA Amplification Using T4 gp32 with T6 H66S Recombinase

This experiment was performed to investigate whether the UvsY-independent amplification would occur when T4 gp32 was used together with T6 H66S UvsX. The general reaction conditions were as described for the experiment depicted in FIG. 52, except that here reactions were conducted using either Rb69 gp32 or 337.5 ng/μl T4 gp32. Where T4 gp32 was used in the presence of UvsY, 30 ng/μl T4 UvsY was used. 1000 copies of human genomic DNA were used per reaction in conjunction with primer ApoB4 and either primer ApoB300 or ApoB3. As shown in FIG. 57, this experiment shows that the UvsY-independent activity of T6 H66S recombinase is still found when T4 gp32, rather than Rb69 gp32, is utilized. The production of clean expected products is less efficient than when using Rb69 gp32, however there can be no doubt that large numbers of recombinationally active filaments are present. It was concluded that DNA amplification plainly occurs when using T4 gp32 in reaction, although, in the terms of correct products, this process is less efficient than if Rb69 gp32 is used.

UvsY-Free DNA Amplification Using T6 H66S and Aeh1 gp32

This experiment was performed to investigate whether the UvsY-independent amplification would occur when Aeh1 gp32 was used together with T6 H66S UvsX. Reaction conditions were the same as described for the experiment depicted in FIG. 52, with the exception that reactions were carried out using 400 ng/μl Rb69 gp32 or 360 ng/μl Aeh1 gp32, and 1000 copies human genomic DNA with primer ApoB4 and either primer ApoB300 or ApoB3. As shown in FIG. 58, the results demonstrate when UvsY was omitted and T6 H66S was used, Aeh1 gp32 was unable to support RPA in producing a correct product. However, some small amount of amplification did occur. It was concluded that, when combined with T6 H66S, Aeh1 promotes only limited DNA amplification. This data, when combined with the data previously described, suggests that the efficiency of UvsY-independent behaviour of T6 H66S RPA reactions is to some extent dependent on gp32 type.

UvsY-Free DNA Amplification Using T4 UvsX

An experiment was performed to investigate whether the presence of UvsY was needed for DNA amplification to occur when using T4 UvsX with Rb69 gp32. These reactions were conducted as described in the experiment depicted in FIG. 52, with the following exceptions: reactions were performed using either T6 H66S UvsX or 123.5 ng/μl T4 UvsX, and 1000 copies of human genomic DNA with primer ApoB4 and either primer ApoB300 or ApoB3. Where T4 UvsX was used with UvsY, 30 ng/μl T4 UvsY was utilized. As shown in FIG. 59, the results demonstrate that in the presence of UvsY, T4 UvsX reactions generate products of the expected size, as when T6 H66S UvsX is used. However, unlike T6 H66S reactions, when UvsY is omitted no amplification products whatsoever are generated. This experiment shows that under the standard conditions employed T4 UvsX, unlike T6 H66S UvsX, is totally dependent on the presence of UvsY protein. This data confirms a large body of earlier evidence, which showed that UvsY and PEG were both obligate components of RPA systems configured with T4 reagents.

An additional experiment was performed to investigate if by using T4 gp32 instead of Rb69 gp32, whether UvsY-deficient T4 UvsX reactions would continue to fail to produce amplification product. The general reaction conditions were as described for the experiment depicted in FIG. 52 with the exception that reactions were performed using either Rb69 gp32 with T6 H66S UvsX or 337 ng/μl T4 gp32 with 123 ng/μl T4 UvsX. 1000 copies of human genomic DNA were used per reaction in conjunction with primer ApoB4 and either primer ApoB300 or ApoB3. Where T4 gp32 and UvsX were used with UvsY, 30 ng/μl T4 UvsY was utilized. As shown in FIG. 60, the results demonstrate that, similar to that shown previously, in the presence of UvsY, reactions utilizing T4 components generate products of the correct size and the absence of UvsY negates this. This data confirms the conclusion that under the standard conditions, T4 UvsX, unlike T6 H66S UvsX, is totally dependent on the presence of UvsY protein. In this case T4 gp32 was employed as the single-stranded DNA binding protein.

Yet another experiment was performed to investigate the requirement for UvsY when using T4 UvsX in RPA amplification/detection reactions that utilize a fluorescent probe system to sense DNA accumulation. In this experiment RPA was performed under the following conditions: 100 mM Potassium acetate, 50 mM Tris.acetate pH 8.3, 14 mM Magnesium acetate, 5 mM dTT, 200 mM dNTPs, 50 mM Creatine phosphate (Calbiochem), 2.5 mM ATP (Roche), 50 ng/μl Creatine Kinase (Roche), amplification primers J1 (120 nM) and K2 (480 nM), 120 nM fluorescent probe BsFlc, 5% PEG 35,000, 43.33 ng/μl Sau Polymerase, 600 ng/μl Rb69 gp32, 120 ng/μl T6 H66S UvsX and 79 ng/μl Rb69 UvsY, where appropriate. Nfo was included at 100 ng/μl. Samples contained either water or 200 copies of B. subtilis genomic DNA, and were either in the presence or absence of Rb69 UvsY. Reactions were established on ice in a 384-well plate, and then transferred to a BIOTEK Flx-800 fluorescence microplate reader with stage set to 38′C at which time measurements were taken periodically from a bottom-reading probe.

As shown in FIG. 61, signal accumulated in a template-dependent manner in reactions configured with T6 H66S recombinase with or without UvsY, and also with reactions containing T4 UvsX in the presence of UvsY. However, in the absence of UvsY, T4 UvsX reactions displayed no DNA amplification capability. It was concluded that under these standard conditions, for DNA amplification to occur, unlike T6 H66S UvsX, T4 UvsX has a strict requirement for UvsY.

An additional experiment was carried out in order to investigate the effects of titrating Rb69 gp32 concentrations on the requirement of T4 UvsX for UvsY. These reactions were conducted as described for the experiment depicted in FIG. 61, with the exception that reactions were performed using amplification primers Sccii35IV (480 nM) and OrfX45a (120 nM), 120 nM fluorescent probe SA Tamra2, 125 ng/μl T4 UvsX and 30 ng/μl T4 UvsY, where appropriate. Rb69 gp32 was used at 400 ng/μl, 600 ng/μl or 800 ng/μl. Samples contained either water or 200 copies of MRSA I genomic DNA, and were either in the presence or absence of Rb69 UvsY. As shown in FIG. 69, DNA amplification occurred in all template samples containing UvsY, regardless of the concentration of Rb69 used. No template sample demonstrated DNA amplification when UvsY was missing. It was concluded that under the standard conditions employed, for DNA amplification to occur, the T4 UvsX protein is dependent on UvsY and that this dependency is not altered by variation of gp32 concentration.

Yet another experiment was carried out to further investigate the requirement of the T4 UvsX protein for UvsY. The reaction conditions used were the same as described for the experiment depicted in FIG. 61, with the following exceptions: reactions were performed using amplification primers Scciii (480 nM) and OrfX45a (120 nM), 120 nM fluorescent probe BsFlc beta, 123.5 ng/μl T4 UvsX, 500 ng/μl Rb69 gp32 and 18 ng/μl Sau Polymerase. Samples contained either water or 10000 copies of 506 bp PCR DNA fragment, and were either in the presence or absence of Rb69 UvsY. As shown in FIG. 70, under these conditions, T4 UvsX reactions efficiently amplify DNA, both in the presence and absence of UvsY. However, DNA amplification in samples that contained UvsY preceded those where UvsY was missing, and at experiment termination more DNA had been amplified in the presence of UvsY than the absence of UvsY. It was concluded that depending upon the conditions employed, T4 UvsX may or may not require the presence of UvsY for DNA amplification to occur. However, even where the conditions allow amplification to occur in the absence of UvsY, the addition of UvsY improves the reaction rate and increases the amplified DNA output.

To further elucidate the requirement of T4 UvsX protein for UvsY, a further experiment was performed. The reaction conditions and samples were those described in FIG. 70. Following reaction completion, each of the samples was purified using the GenElute PCR cleanup kit (Sigma) and visualized using gel electrophoresis. As shown in FIG. 71, gel electorphoresis can be used as an additional method (process) of visualizing the data collected for DNA amplification using RPA, such as the experiment described in FIG. 70. The results shown in FIG. 71 further demonstrate that under these conditions, T4 UvsX enables DNA amplification to occur both in the presence and absence of UvsY. However, as described for the experiment depicted in FIG. 70, more DNA was amplified in the presence of UvsY than in the absence of UvsY. These results confirm that under certain conditions, T4 UvsX can support DNA amplification in the absence of UvsY, however the amount of DNA amplification is improved in the presence of UvsY.

UvsY-Free DNA Amplification Using T6 UvsX

This experiment was performed to determine whether the unmodified T6 UvsX protein exhibits the capacity to amplify DNA in the absence of UvsY. The reaction conditions used were as described for the experiment depicted in FIG. 52, with the exception that the reactions were performed using T6 H66S UvsX or 120 ng/μl T6 UvsX, and 1000 copies of human genomic DNA with primer ApoB4 and either primer ApoB300 or ApoB3. As shown in FIG. 62, one of the two amplicons examined was efficiently amplified, while one was not, in the absence of UvsY. Furthermore, the relative efficiency of amplification of fragments between T6 and T6 H66S recombinase with or without UvsY were variant. While one cannot exclude preparation-dependent variations in between the recombinase proteins, this data is consistent with the suggestion that the unmodified and modified recombinase demonstrate variant activities as indicated earlier. It was concluded that in the absence of UvsY, DNA amplification can occur with T6 UvsX, although the efficiency to do this is different from T6 H66S UvsX.

UvsY-Free DNA Amplification Using Rb69 UvsX

This experiment investigated whether Rb69 UvsX requires UvsY for efficient amplification. The reactions were conducted as described for the experiment depicted in FIG. 52, with the exception that the reactions were performed using T6 H66S UvsX or 120 ng/μl Rb69 UvsX, 400 ng/μl Rb69 gp32, and 1000 copies of human genomic DNA with primer ApoB4 and either primer ApoB300 or ApoB3. As shown in FIG. 63, no amplification was seen in the absence of UvsY consistent with a strict dependence on the presence of UvsY under the conditions employed. Even with UvsY present, amplification was poor, so some caution should be placed on the interpretation. Without intending to be bound by any theory, the simplest explanation is that like with T4 UvsX, UvsY is required to achieve filament-loading levels required for effective and sensitive amplification. It was concluded that under the standard conditions employed, Rb69 UvsX is likely to require UvsY for efficient DNA amplification to be achieved.

UvsY-Free DNA Amplification Using Aeh1 UvsX

This experiment was performed to address whether Aeh1 UvsX requires UvsY for efficient amplification. Reaction conditions were as described for the experiment depicted in FIG. 52, with the exception that the reactions were carried out using 400 ng/μl Rb69 gp32 for reactions with T6 H66S UvsX, and for reactions with Aeh1: 500 ng/μl Rb69 gp32 UvsX, 200 ng/μl Aeh1 UvsX and 80 ng/μl Aeh1 UvsY, where UvsY was included. 1000 copies of human genomic DNA were used per reaction in conjunction with primer ApoB4 and either primer ApoB300 or ApoB3. As shown in FIG. 64, no amplification was seen in the absence of UvsY where Aeh1 proteins were used, while with the presence of UvsY, correct sized products were evident. It was concluded that Aeh1 proteins are unable to undergo DNA amplification in the absence of UvsY, consistent with a strict dependence on the presence of UvsY under the conditions employed.

UvsY-Free DNA Amplification Using Modified Rb69 UvsX (T6 DNA Binding Loop2, Modification of Histidine 64 to Serine, and Modified C Terminus (LDEx2))

This experiment was performed to investigate whether modified Rb69 UvsX containing the DNA binding loop2 of T6UvsX requires UvsY for efficient amplification, and to determine whether the variant DNA binding loop2 of T6 recombinase accounted for the UvsY-independent activity of T6 recombinases. Reaction conditions employed were as described for the experiment depicted in FIG. 52, with the following exceptions: reactions were performed using 400 ng/μl Rb69 gp32 and either T6 H66S UvsX or 120 ng/μl T6 H64S 2xLDE UvsX. 1000 copies of human genomic DNA were used per reaction in conjunction with primer ApoB4 and either primer ApoB300 or ApoB3. As shown in FIG. 65, no amplification was seen in the absence of UvsY consistent with dependence on the presence of UvsY under the conditions employed.

Without intending to be bound by any theory, one interpretation of this experiment is that the DNA binding loop 2, in isolation, may be insufficient to confer UvsY-independent activity on hybrid recombinases. However caution should be exercised as poor amplification was observed with this protein even in the presence of UvsY. It was concluded that, under the standard conditions employed, T6 H64S 2xLDE UvsX is likely to require UvsY for efficient DNA amplification to be achieved.

Example 16 gp32 Activity

The ability to measure the effectiveness of gp32 in regulating the cutting rate proves to be a very accurate approach to assess gp32 activity, something which has been historically difficult to assess. An experiment was performed to demonstrate a useful assay for the activity of gp32 preparations. Experimental conditions were as follows: reactions were performed in 50 μl volume; final concentration of probe (SA-Tamra2; 5′-tgttaattgagcaagtgtatagagcattraygabtatgcgtggag-3′ (SEQ ID NO:125), here y=thf, b=BHQ2-dT, r=TAMRA-dT, 3′=Bio-TEG) was 100 nM; Rb69 pg32 was used at final concentration of 0, 40, 50, 63, 83, 100, 125, 167, or 250 ng/μl; Nfo was present at 33 ng/μl; buffer conditions were 20 mM Tris-acetate, 50 mM potassium acetate (pH 7.9), 10 mM Magnesium Acetate, 1 mM Dithiothreitol.

As depicted in FIG. 66, the results of this experiment show that a single-stranded probe which contains a fluorophore and quencher separated by a tetrahydrofuran residue (THF) can be rapidly cut by an excess of Nfo nuclease when present in an aqueous buffered solution, and in the absence of gp32 protein. This activity was robust under these conditions despite claims in the literature that Nfo targets only duplex DNA substrates. Without intending to be bound by any theory, the activity may arise by formation of transient duplex structures, hairpins and the like, under the conditions used here. This activity was entirely suppressed by an excess of gp32 protein when included in the reaction mixture. When the mass of gp32 was progressively decreased, cutting activity was once again detected (monitored by increasing fluorescence over time) and the rate of cutting was regulated by the mass of gp32 added at these limiting final concentrations. Furthermore, by setting the concentration of gp32 at limiting levels in experiments it was possible to assess consequences of a variety of manipulations such as the effects of competitor nucleic acids or temperature on gp32 behaviour and turnover.

Biochemical Distinction Among Different Species of gp32 Molecules

An experiment was performed to assess whether gp32 molecules from different species of origin were biochemically distinct from one another. Experimental conditions were as follows: reactions were performed in 50u1 volume; final concentration of probe (SA-Tamra2; 5′-tgttaattgagcaagtgtatagagcattraygabtatgcgtggag-3′ (SEQ ID NO:126), here y=thf, b=BHQ2-dT, r=TAMRA-dT, 3′=Bio-TEG) was 100 nM; Rb69 pg32 was used at final concentration of 80 ng/μl, Nfo was present at 33 ng/μl; after 350 sec either water, dsDNA (550 ng human genomic DNA; i.e. approximately 10× mass of oligonucleotide probe) or ssDNA (28 pmol oligonucleotide of sequence 5′ ctgtattagaagtacatgctgatcaagtgaca-3′ (SEQ ID NO:127)) was added; buffer conditions were 20 mM Tris-acetate, 50 mM potassium acetate (pH 7.9), 10 mM Magnesium Acetate, 1 mM Dithiothreitol. Measurements were made in a fluorometer manufactured by Embedded System Engineering (ESE,GmbH) with LED excitation of 520 nM and emission at 585 nM.

Initially, a concentration of gp32 was established which permitted only a very low cutting activity by Nfo nuclease on the fluorophore/quencher probe. At this concentration the availability of gp32 was limited to a minimal quantity for substantial probe protection, and under these conditions it was possible to assess very sensitively whether gp32 was partitioned away from the probe in competition experiments. After monitoring the slow probe cutting for a while, excess double-stranded DNA or single-stranded oligonucleotides were added to assess whether this affected the distribution of gp32 on the probe. In all cases the addition of excess in single-stranded oligonucleotide lead to a sudden and pronounced increase in fluorescence and hence probe cutting. However, rather interestingly, it was discovered that T4 gp32 was strongly influenced by the addition of the duplex DNA as cutting became very pronounced indicating loss of gp32 from the probe DNA, while Rb69 and Aeh1 gp32 species showed only slight increases in cutting. Clearly Rb69 and Aeh1 gp32 molecules differentiated and partitioned much more effectively in favour of single-stranded DNA than T4 gp32. The results are depicted in FIG. 67, which shows that T4 and Rb69 gp32 molecules are biochemically distinct in regard to partitioning between single-stranded and duplex DNAs.

Temperature Limits for Different gp32 Species

An experiment was performed using the probe protection assay to assess at what upper temperature different species of gp32 failed to function correctly. Experimental conditions were as follows: reactions were performed in 50 μl volume; final concentration of probe (SA-Tamra2; 5′-tgttaattgagcaagtgtatagagcattraygabtatgcgtggag-3′ (SEQ ID NO:128), where y=thf, b=BHQ2-dT, r=TAMRA-dT, 3′=Bio-TEG) was 100 nM; Rb69 pg32 was used at final concentration of 80 ng/μl, Nfo was present at 33 ng/μl; after 350 sec the temperature was gradually raised (see graph); buffer conditions were 20 mM Tris-acetate, 50 mM potassium acetate (pH 7.9), 10 mM Magnesium Acetate, 1 mM Dithiothreitol. Measurements were made in a fluorometer manufactured by Embedded System Engineering (ESE,GmbH) with LED excitation of 520 nM and emission at 585 nM.

Concentrations of gp32 were used that lead to a situation in which gp32 were just limiting with regard to probe protection. Reactions were then continuously monitored after a heat source was applied such that temperature gradually increased in the reaction environment. Indicated temperatures referred to those read from a thermocouple in the fluorescent probe device utilized which was close to the tube containing the reaction and thus a good indicator of the reaction temperature. As shown in FIG. 68, there were differences in upper temperature activity limits for different gp32 species. As the temperature rises the slope of the fluorescence curves initially remained constant, but at some point began to increase. Without intending to be bound by any theory, this evidence indicated that the gp32 was losing its effectiveness because the protein was becoming structurally unstable. Support for this interpretation rather than an interpretation in which Nfo activity progressively increases, is provided by the fact that T4 gp32 does not show any rate changes until relatively high temperatures, while when other gp32 molecules are used, changes begin much earlier. In particular it was noted that Aeh1 gp32 became highly ineffective at about 40° C., and displayed a pronounced loss of activity in the assay above this point. Rb69 gp32 also appeared to be less tolerant of higher temperatures than T4 gp32 and became partially affected by about 42° C. T4 gp32 is much more resistant and was still functioning at a temperature of at least 47° C.

The data describes herein supports the discovery of novel, diverse, hybrid and engineered recombinase enzymes and the utility of such enzymes for carrying out RPA reactions. The data further supports the identification of optimal conditions for carrying out RPA reactions using the novel, diverse, hybrid and engineered recombinase agents described herein and associated recombination factors. While specific embodiments of the subject invention have been discussed, the above specification is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this specification. The appendant claims are not intended to claim all such embodiments and variations, and the full scope of the invention should be determined by reference to the claims, along with their full scope of equivalents, and the specification, along with such variations.

All publications, patent applications, and patents mentioned herein, including those items listed below, are hereby incorporated by reference in their entireties as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control.

REFERENCES

-   Amasino R. M., Acceleration of nucleic acid hybridization rate by     polyethylene glycol. Anal Biochem, Volume 152, Issue 2, 304-7, Feb.     1, 1986. Armes N. A. and Stemple D. L., Recombinase Polymerase     Amplification, U.S. patent application Ser. No. 10/371,641.     Benedict R. C. and Kowalczykowski S. C. Increase in the DNA strand     assimilation activity of RecA protein by removal of the C terminus     and structure-function studies of the resulting protein fragment. J.     Biol. Chem. 1988 Oct. 25; 263(30):15513-20. Chan E. W., Dale P. J.,     Greco I. L., Rose J. G., O'Connor T. E., Biochim Biophys Acta,     Volume 606, Issue 2, 353-61, Feb. 29, 1980. Eggler A. L., Lusetti S.     L., Cox M. M. The C terminus of the Escherichia coli RecA protein     modulates the DNA binding competition with single-stranded     DNA-binding protein. J. Biol. Chem. 2003 May 2; 278(18):16389-96.     Ellouze C., Takahashi M., Wittung P., Mortensen K., Schnarr M.,     Norden B. Eur. J. Biochem. 1995 Oct. 15; 233(2):579-83. Formosa T.     and Alberts B. M. Purification and characterization of the T4     bacteriophage UvsX protein. J. Biol. Chem. 1986 May 5; 261     (13):6107-18. Giedroc D. P., Gin H. W, Khan R., King G. C., Chen K.     Zn(II) coordination domain mutants of T4 gp32 protein. Biochemistry.     1992 Jan. 28; 31 (3):765-74. Giedroc D. P., Keating K. M.,     Williams K. R., and Coleman J. E. The function of zinc in gene 32     protein from T4. Biochemistry 1987 Aug. 25; 26(17):5251-9.     Layery P. E. and Kowalczykowski S. C., J. Biol. Chem., Vol. 267,     Issue 13, 9307-14, May 5, 1992. Lerman L. S., A transition to a     Compact Form of DNA in Polymer Solutions. Proc Natl Acad Sci USA.     1971 April; 68(8):1886-1890. Lusetti S. L., Shaw J. J., Cox M. M.     Magnesium ion-dependent activation of the RecA protein involves the     C terminus. J. Biol. Chem. 2003 May 2; 278(18):16389-96.     Malkov V. A. and Camerini-Otero R. D. Photocross-links between     single-stranded DNA and Escherichia coli RecA protein map to loops     L1 (amino acid residues 157-164) and L2 (amino acid residues     195-209). J. Biol. Chem. 1995 Dec. 15, Volume 270, Issue 50,     30230-3. Minton A. P. The Influence of Macromolecular Crowding and     Macromolecular Confinement on Biochemical Reactions in Physiological     Media. J. Biol. Chem., Vol. 276, Issue 14, 10577-10580, Apr.     6, 2001. Naimushin A. N., Quach M., Fujimoto B. S., Schurr J. M.     Effect of polyethylene glycol on the supercoiling free energy of     DNA. Biopolymers. 2001, Volume 58, Issue 2, 204-17. Nadler S. G.,     Roberts W. J., Shamoo Y., Williams K. R. A novel function for     Zinc(II) in a nucleic acid-binding protein. Contribution of Zinc(II)     toward the cooperativity of bacteriophage T4 gp32 protein     binding. J. Biol. Chem. 1990 Jun. 25; 265(18):10389-94. Qiu H. and     Giedroc D. P. Effects of substitution of proposed Zn(II) ligand     His81 or His64 in phage gp32 protein:spectroscopic evidence for a     novel zinc coordination complex. Biochemistry 1994 Jul. 5;     33(26):8139-48. Rivas G., Ferrone F., Herzfeld J. Life in a crowded     world—Workshop on the Biological Implications of Macromolecular     Crowding. EMBO reports 5, 1, 23-27 (2004)     doi:10.1038/sj.embor.7400056 Published online: 19 Dec. 2003.     Story R. M., Bishop D. K., Kleckner N., Steitz, T. A. Structural     relationship of bacterial RecA proteins to recombination proteins     from bacteriophage T4 and yeast. Science. 1993 Mar. 26,     259(5103):1892-6. Voloshin O. N., Wang L., Camerini-Otero R. D.     Homologous DNA pairing Promoted by a 20-Amino Acid Peptide Derived     from RecA. Science 10 May 1996. Vol 272 Number 5263, pages 868-872.     Voloshin O. N., Wang L., Camerini-Otero R. D. The homologous pairing     domain of RecA also mediates the allosteric regulation of DNA     binding and ATP hydrolysis: a remarkable concentration of functional     residues. J. Mol. Biol. 2000 Nov. 10; 303(5):709-20. Walker J. E.,     Saraste M., Runswick M., and Gay N. J. 1982 EMBO J. Volume 1. Pages     945-51. Zarling, D. A., Sena E. P., Green C. J., U.S. Pat. No.     5,223,414 filed May 7, 1990. Zimmerman SB and Harrison B.     Macromolecular crowding increases binding of DNA polymerase to DNA:     an adaptive effect. Proc Natl Acad Sci USA. 1987 April;     84(7):1871-5. Zinchenko A. A. and Yoshikawa, K. Biophysical Journal.     June 2005. 

1-25. (canceled)
 26. A method, comprising: (a) contacting UvsX, UvsY, and gp32 proteins with first and second single stranded nucleic acid primers specific for a double stranded target nucleic acid molecule to provide first and second nucleoprotein primers, the UvsX, UvsY, and gp32 each being derived from a myoviridae phage, and at most two of the UvsX, UvsY, and gp32 proteins being T4 phage proteins; (b) contacting the first nucleoprotein primer with the double stranded target nucleic acid molecule to create a first D loop structure at a first portion of the double stranded target nucleic acid molecule; (c) contacting the second nucleoprotein primer with the double stranded target nucleic acid molecule to create a second D loop structure at a second portion of the double stranded target nucleic acid molecule so that the 3′ ends of the first and second nucleic acid primers are oriented toward each other on the same double stranded target nucleic acid molecule without completely denaturing the target nucleic acid molecule; and (d) extending the 3′ end of the first and second nucleoprotein primers with one or more polymerases capable of strand displacement synthesis and dNTPs to provide first and second double stranded target nucleic acid molecules and first and second displaced strands of nucleic acid.
 27. The method of claim 26, further comprising repeating (b) through (d).
 28. The method of claim 26, wherein the first and second displaced strands of nucleic acid hybridize to each other after (d) to form a third double stranded target nucleic acid molecule.
 29. The method of claim 26, wherein the myoviridae phage is selected from the group consisting of T4, T2, T6, Rb69, Aeh1, KVP40, Acinetobacter phage 133, Aeromonas phage 65, cyanophage P-SSM2, cyanophage PSSM4, cyanophage S-PM2, Rb14, Rb32, Aeromonas phage 25, Vibrio phage nt-1, phi-1, Rb16, Rb43, phage 44RR2.8t, Rb49, phage Rb3 and phage LZ2.
 30. The method of claim 26, wherein the UvsX, UvsY and gp32 are selected from the group consisting of: (a) Rb69 UvsX, Rb69 UvsY and Rb69 gp32; (b) Aeh1 UvsX, Aeh1 UvsY and Rb69 gp32; (c) T4 UvsX, T4 UvsY and Rb69 gp32; and (d) T4 UvsX, Rb69 UvsY and T4 gp32.
 31. The method of claim 26, wherein the UvsX, UvsY, and gp32 are native, hybrid, or mutant proteins from the same or different myoviridae phage sources.
 32. The method of claim 31, wherein the hybrid protein comprises one or more amino acid residues from two different species of myoviridae phages to yield a protein with improved performance characteristics in the method.
 33. The method of claim 31, wherein the UvsX is a mutant UvsX.
 34. The method of claim 33, wherein the mutant UvsX is an Rb69 UvsX comprising at least one modification the Rb69 UvsX amino acid sequence, wherein the modification is selected from the group consisting of: an amino acid which is not histidine at position 64; a serine at position 64; the addition of one or more glutamic acid residues at the C-terminus; the addition of one or more aspartic acid residues at the C-terminus; and a combination thereof.
 35. The method of claim 33, wherein the mutant UvsX is a T6 UvsX having at least one modification in the T6 UvsX amino acid sequence, wherein the modification is selected from the group consisting of: an amino acid which is not histidine at position 66; a serine at position 66; the addition of one or more glutamic acid residues at the C-terminus; the addition of one or more aspartic acid residues at the C-terminus; and a combination thereof.
 36. The method of claim 32, wherein the hybrid protein is a UvsX protein comprising at least one region which comprises an amino acid sequence from a different UvsX species.
 37. The method of claim 36, wherein the at least one region is the DNA-binding loop-2 region of UvsX.
 38. The method of claim 26, wherein the method is performed in the presence of a crowding agent selected from the group consisting of polyethylene glycol, polyethylene oxide, polystyrene, Ficoll, dextran, PVP, and albumin, such that the crowding agent stimulates amplification.
 39. The method of claim 38, wherein the crowding agent has a molecular weight of less than 200,000.
 40. The method of claim 38, wherein the crowding agent is present in an amount of about 0.5% to about 15% w/v.
 41. The method of claim 26, wherein the polymerase is a large fragment polymerase selected from the group consisting of E. coli Pol I, Bacillus subtilis Pol I, Staphylococcus aureus Pol I, and homologues thereof.
 42. The method of claim 26, wherein the method is performed in the presence of heparin.
 43. The method of claim 26, wherein the first or second nucleic acid primer is a blocked primer, and the method is performed in the presence of E. coli exonuclease III or E. coli endonuclease IV.
 44. The method of claim 26, wherein the method is performed in the presence of about 1 mM to about 8 mM divalent manganese ions.
 45. The method of claim 26, wherein the UvsX protein comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 105, SEQ ID NO: 106, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122; or the UvsY protein comprises an amino acid sequence of SEQ ID NO: 123 or SEQ ID NO:
 124. 46. The method of claim 45, wherein the UvsX comprises the amino acid sequence SEQ ID NO: 105, the UvsY is a Rb69 UvsY, the gp32 protein is a Rb69 gp32, and the one or more polymerases capable of strand displacement synthesis is a DNA polymerase I.
 47. The method of claim 26, wherein the myoviridae phage is Phage
 31. 48. A method, comprising: (a) contacting UvsX, UvsY, and gp32 proteins with first and second single stranded nucleic acid primers specific for a double stranded target nucleic acid molecule to provide first and second nucleoprotein primers, the UvsX, UvsY, and gp32 each being derived from a myoviridae phage selected from the group consisting of T4, T2, T6, Rb69, Aeh1, KVP40, Acinetobacter phage 133, Aeromonas phage 65, cyanophage P-SSM2, cyanophage PSSM4, cyanophage S-PM2, Rb14, Rb32, Aeromonas phage 25, Vibrio phage nt-1, phi-1, Rb16, Rb43, Phage 31, phage 44RR2.8t, Rb49, phage Rb3, and phage LZ2, and at most two of the UvsX, UvsY, and gp32 proteins being T4 phage proteins; (b) contacting the first nucleoprotein primer with the double stranded target nucleic acid molecule to create a first D loop structure at a first portion of the double stranded target nucleic acid molecule; (c) contacting the second nucleoprotein primer with the double stranded target nucleic acid molecule to create a second D loop structure at a second portion of the double stranded target nucleic acid molecule so that the 3′ ends of the first and second nucleic acid primers are oriented toward each other on the same double stranded target nucleic acid molecule without completely denaturing the target nucleic acid molecule; and (d) extending the 3′ end of the first and second nucleoprotein primers with one or more polymerases capable of strand displacement synthesis and dNTPs to provide first and second double stranded target nucleic acid molecules and first and second displaced strands of nucleic acid.
 49. The method of claim 48, further comprising repeating (b) through (d).
 50. The method of claim 48, wherein the first and second displaced strands of nucleic acid hybridize to each other after (d) to form a third double stranded target nucleic acid molecule.
 51. The method of claim 48, wherein the UvsX, UvsY and gp32 are selected from the group consisting of: (a) Rb69 UvsX, Rb69 UvsY and Rb69 gp32; (b) Aeh1 UvsX, Aeh1 UvsY and Rb69 gp32; and (c) T4 UvsX, T4 UvsY and Rb69 gp32.
 52. The method of claim 48, wherein the UvsX is T4 UvsX, the UvsY is Rb69 UvsY, and the gp32 is T4 gp32.
 53. The method of claim 48, wherein the UvsX, UvsY, and gp32 are native, hybrid, or mutant proteins from the same or different myoviridae phage sources.
 54. The method of claim 53, wherein the hybrid protein comprises one or more amino acid residues from two different species of myoviridae phages to yield a protein with improved performance characteristics in the method.
 55. The method of claim 53, wherein the UvsX is a mutant UvsX.
 56. The method of claim 55, wherein the mutant UvsX is an Rb69 UvsX comprising at least one modification in the Rb69 UvsX amino acid sequence, wherein the modification is selected from the group consisting of: an amino acid which is not histidine at position 64; a serine at position 64; the addition of one or more glutamic acid residues at the C-terminus; the addition of one or more aspartic acid residues at the C-terminus; and a combination thereof.
 57. The method of claim 55, wherein the mutant UvsX is a T6 UvsX having at least one modification in the T6 UvsX amino acid sequence, wherein the modification is selected from the group consisting of: an amino acid which is not histidine at position 66; a serine at position 66; the addition of one or more glutamic acid residues at the C-terminus; the addition of one or more aspartic acid residues at the C-terminus; and a combination thereof.
 58. The method of claim 54, wherein the hybrid protein is a UvsX protein comprising at least one region which comprises an amino acid sequence from a different UvsX species.
 59. The method of claim 58, wherein the at least one region is the DNA-binding loop-2 region of UvsX.
 60. The method of claim 48, wherein the method is performed in the presence of a crowding agent selected from the group consisting of polyethylene glycol, polyethylene oxide, polystyrene, Ficoll, dextran, PVP, and albumin, such that the crowding agent stimulates amplification.
 61. The method of claim 60, wherein the crowding agent has a molecular weight of less than 200,000.
 62. The method of claim 60, wherein the crowding agent is present in an amount of about 0.5% to about 15% w/v.
 63. The method of claim 48, wherein the polymerase is a large fragment polymerase selected from the group consisting of E. coli Pol I, Bacillus subtilis Pol I, Staphylococcus aureus Pol I, and homologues thereof.
 64. The method of claim 48, wherein the method is performed in the presence of heparin.
 65. The method of claim 48, wherein the first or second nucleic acid primer is a blocked primer, and the method is performed in the presence of E. coli exonuclease III or E. coli endonuclease IV.
 66. The method of claim 48, wherein the method is performed in the presence of about 1 mM to about 8 mM divalent manganese ions.
 67. The method of claim 48, wherein the UvsX protein comprises an amino acid sequence selected from the group consisting of: SEQ ID NO: 105, SEQ ID NO: 106, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, SEQ ID NO: 117, SEQ ID NO: 118, SEQ ID NO: 119, SEQ ID NO: 120, SEQ ID NO: 121, and SEQ ID NO: 122; or the UvsY protein comprises an amino acid sequence of SEQ ID NO: 123 or SEQ ID NO:
 124. 68. The method of claim 67, wherein the UvsX comprises the amino acid sequence SEQ ID NO:105, the UvsY is a Rb69 UvsY, the gp32 protein is a Rb69 gp32, and the one or more polymerases capable of strand displacement synthesis is a DNA polymerase I.
 69. A method, comprising: (a) contacting UvsX and gp32 proteins with first and second single stranded nucleic acid primers specific for a double stranded target nucleic acid molecule to provide first and second nucleoprotein primer, the UvsX and gp32 each being derived from a myoviridae phage, and at most one of the UvsX and gp32 proteins are T4 phage proteins; (b) contacting the first nucleoprotein primer to the double stranded target nucleic acid molecule to create a first D loop structure at a first portion of the double stranded target nucleic acid molecule; (c) contacting the second nucleoprotein primer to the double stranded target nucleic acid molecule to create a second D loop structure at a second portion of the double stranded target nucleic acid molecule so that the 3′ ends of the first and second nucleic acid primers are oriented toward each other on the same double stranded target nucleic acid molecule without completely denaturing the target nucleic acid molecule; and (d) extending the 3′ ends of the first and second nucleoprotein primers with one or more polymerases capable of strand displacement synthesis and dNTPs to generate first and second double stranded target nucleic acid molecules and first and second displaced strands of nucleic acid, wherein the method is performed in the absence of UvsY.
 70. The method of claim 69, further comprising repeating (b) through (d).
 71. A method, comprising: (a) contacting UvsX, UvsY, and gp32 proteins with a first single stranded nucleic acid primer specific for a double stranded target nucleic acid molecule to provide a population of first nucleoprotein primer, the UvsX, UvsY, and gp32 each being derived from a myoviridae phage, and at most two of the UvsX, UvsY and gp32 proteins are T4 phage proteins; (b) contacting the first nucleoprotein primer with the double stranded target nucleic acid molecule to provide a first D loop structure at a first portion of the double stranded target nucleic acid molecule without completely denaturing the target nucleic acid molecule; (c) extending the 3′ end of the first nucleoprotein primer with one or more polymerases capable of strand displacement synthesis and dNTPs to provide a double stranded target nucleic acid molecule and a displaced strand of nucleic acid molecule; (d) hybridizing a second single stranded nucleic acid primer with the displaced strand of nucleic acid molecule to form a hybridized second single stranded nucleic acid primer; and (e) elongating the hybridized second single stranded nucleic acid primer to provide a double stranded target nucleic acid molecule.
 72. The method of claim 71, further comprising repeating (b) through (e). 